Patent application title: SHORT-FLUX PATH MOTORS / GENERATORS

Abstract:

According to one embodiment of the present invention, an electric machine
includes a stator and a rotor. The stator includes a stator pole
including a first leg and a second leg, and a gap defined between the
first and second legs. The rotor includes a rotor pole. The rotor is
configured to rotate relative to the stator such that the rotor pole
rotates through the gap defined between the first and second legs of the
stator pole. The stator pole includes a laminar stator pole structure
including multiple lamination layers.

Claims:

1. An electric machine, comprising:a stator having a stator pole including
a first leg and a second leg, and a gap defined between the first and
second legs; anda rotor including a rotor pole, the rotor configured to
rotate relative to the stator such that the rotor pole rotates through
the gap defined between the first and second legs of the stator
pole;wherein the stator pole includes a laminar stator pole structure
including multiple lamination layers.

2. An electric machine according to claim 1, wherein:the shape of the
stator pole defines a bend; andthe multiple lamination layers of the
laminar stator pole structure extend around the bend defined by the
stator pole.

3. An electric machine according to claim 1, wherein:the rotor rotates
relative to the stator generally in a first plane; andthe rotor pole
includes a laminar rotor pole structure including lamination layers
formed in planes perpendicular to the first plane.

4. An electric machine according to claim 1, wherein:the rotor pole
includes a laminar rotor pole structure including multiple lamination
layers; andthe lamination layers of the laminar rotor pole structure are
aligned generally parallel with the lamination layers of a first portion
of the laminar stator pole structure when the laminar rotor pole
structure passes nearby the first portion of the laminar stator pole
structure during rotation of the rotor.

5. An electric machine according to claim 1, wherein:the laminar stator
pole structure includes a leg portion and end portion; andthe end portion
of the laminar stator pole structure is cut at a non-perpendicular angle
such that an exposed area of the end portion is greater than a
perpendicular cross-sectional area of the leg portion of the laminar
stator pole structure.

6. An electric machine according to claim 1, wherein the laminar stator
pole structure is formed by:wrapping a layer of material around a mandrel
multiple times to form a continuous multi-layered structure; andcutting
out a portion of the continuous multi-layered structure to define two
legs and a gap between the two legs.

7. An electric machine according to claim 6, wherein the laminar stator
pole structure is formed by cutting out a portion of the continuous
multi-layered structure at a non-right angle relative to the continuous
multi-layered structure proximate the cutting location.

8. An electric machine according to claim 1, wherein:the stator pole is
generally U-shaped including a first leg and a second leg;the laminar
stator pole structure extends along the length of the U-shaped stator
pole from an end portion of the first leg to an end portion of the second
leg;proximate an end portion of the first leg, the laminar stator pole
structure turns inward toward the end portion of the second leg;
andproximate an end portion of the second leg, the laminar stator pole
structure turns inward toward the end portion of the first leg.

9. An electric machine, comprising:a housing;a stator having a stator pole
including a first leg and a second leg; anda rotor including a rotor
pole, the rotor configured to rotate relative to the stator;wherein at
least one of the stator and the rotor is adjustably coupled to the
housing to allow a distance between the stator pole and the rotor pole to
be adjusted.

10. An electric machine according to claim 9, wherein the rotor pole
comprises a blade configured to rotates through a gap defined between the
first and second legs of the stator pole.

11. An electric machine according to claim 9, wherein:the rotor pole
comprises a blade configured to rotates through a gap defined between the
first and second legs of the stator pole; andat least one of the stator
and the rotor is adjustably coupled to the housing to allow an area of
overlap between the rotor blade and the first and second legs of the
stator pole to be adjusted.

12. An electric machine according to claim 9, wherein the stator is
adjustably coupled to the housing such that the stator may be adjusted in
an axial direction toward or away from a point about which the rotor
rotates.

14. An electric machine according to claim 13, wherein:the rotor rotates
relative to the stator generally in a first plane; andthe laminar rotor
pole structure includes lamination layers formed in planes perpendicular
to the first plane.

15. An electric machine according to claim 13, wherein the lamination
layers of the laminar rotor pole structure are aligned generally parallel
with the lamination layers of a first portion of the laminar stator pole
structure when the laminar rotor pole structure passes nearby the first
portion of the laminar stator pole structure during rotation of the
rotor.

16. An electric machine, comprising:a first stator having a first
perimeter and a plurality of first stator poles arranged around the first
perimeter, each first stator pole including a first leg and a second
leg;a first rotor configured to rotate relative to the first stator
around a first axis;a second stator having a second perimeter and a
plurality of second stator poles arranged around the second perimeter,
each second stator pole including a first leg and a second leg; anda
second rotor configured to rotate relative to the second stator around
the first axis;wherein the second stator is rotationally offset from the
first stator about the first axis such that the second stator poles are
offset from the first stator poles.

17. An electric machine according to claim 16, wherein:the plurality of
first stator poles of the first stators are arranged around the first
perimeter at intervals of x degrees; andthe second stator is rotationally
offset from the first stator about the first axis by x/2 degrees.

18. An electric machine according to claim 16, wherein:the first rotor
includes a plurality of first rotor blades, each first rotor blade
including two legs; andthe second rotor includes a plurality of second
rotor blades, each second rotor blade including two legs.

19. An electric machine according to claim 16, wherein:each first stator
poles and each second stator pole may be in an energized state or a
de-energized state at any given time;at a particular time instant during
the operation of the electric machine, all of the first stator poles are
in a de-energized state; andat the particular time instant, at least one
of the second stator poles is in an energized state.

20. An electric machine according to claim 16, wherein:each first stator
poles and each second stator pole may be in an energized state or a
de-energized state at any given time;during first predetermined time
intervals:all of the first stator poles are in a de-energized state;
andat least one of the second stator poles is in an energized state;
andduring second predetermined time intervals:all of the second stator
poles are in a de-energized state; andat least one of the first stator
poles is in an energized state.

21. An electric machine, comprising:a stator having a plurality of stator
pairs arranged around a stator perimeter, each stator pair including two
legs; anda rotor having a plurality of rotor blades arranged around a
rotor perimeter, each rotor blade including two legs;wherein the rotor
rotates relative to the stator; andwherein at least three stator pairs
are energized simultaneously to generate magnetic circuits with at least
three corresponding rotor blades.

23. An electric machine according to claim 21, wherein the stator includes
at least 12 stator pairs arranged around the stator perimeter.

24. An electric machine according to claim 21, wherein a first stator pair
shares a particular leg with an adjacent second stator pair such that the
particular leg is used as one of the two legs of the first stator pair
and also as one of the two legs of the second stator pair.

25. An electric machine according to claim 21, wherein:the stator includes
a shared leg that is shared between two adjacent stator pairs; anda wire
coil associated with the shared leg is used for energizing the adjacent
stator pairs at different times.

26. An electric machine according to claim 21, wherein at least four
stator pairs are energized at every instance during a 360 degree rotation
of the rotor.

27. An electric machine, comprising:a stator having a plurality of stator
pairs arranged around a stator perimeter, each stator pair including two
legs; anda rotor having a plurality of rotor blades arranged around a
rotor perimeter, each rotor blade including two legs;wherein all of the
plurality of stator pairs are energized simultaneously and de-energized
simultaneously, in an repeating manner, in order to cause the rotor to
rotate relative to the stator.

29. An electric machine according to claim 27, wherein the stator includes
a plurality of shared legs that are shared between adjacent stator pairs
around the stator perimeter.

30. An electric machine according to claim 27, wherein the rotor includes
a plurality of shared legs that are shared between adjacent rotor blades
around the rotor perimeter.

31. An electric machine according to claim 27, wherein the number of
stator pairs is equal to the number of rotor blades.

32. An electric machine according to claim 27, wherein:the stator
comprises an annular portion and a plurality of shared legs extending
from the annular portion and spaced equidistant from each other; anda
wire coil is disposed on each of the plurality of shared legs.

33. An electric machine, comprising:a stator having a plurality of stator
pairs, each stator pair including two legs defining a gap between the two
legs; anda rotor having a plurality of rotor blades including a permanent
magnet;wherein the rotor is configured to rotate relative to the stator
such that the rotor blade rotate through the gaps between the two legs of
each stator pair.

35. An electric machine according to claim 33, wherein the number of
stator pairs is equal to the number of rotor blades.

36. An electric machine according to claim 33, wherein:each rotor blades
includes a permanent magnet having a north or south polarity; andthe
plurality of rotor blades are arranged around a rotor perimeter such that
the permanent magnets are arranged in an alternating manner between north
and south polarity.

37. An electric machine according to claim 33, wherein:during a first time
interval, a first half of the stator pairs are energized with a north
polarity and a second half of the stator pairs are energized with a south
polarity;during a second time interval, the first half of the stator
pairs are energized with a south polarity and a second half of the stator
pairs are energized with a north polarity; andthe first and second time
intervals repeat in an alternating manner during operation of the
electric machine.

38. An electric machine according to claim 33, wherein the plurality of
rotor blades are positioned substantially immediately adjacent each other
around a perimeter of the rotor.

39. An electric machine, comprising:a stator including a stator pole; anda
rotor including a rotor pole, the rotor configured to rotate relative to
the stator; anda housing configured to house a fluid for cooling the
stator, the housing including a housing wall;wherein a first portion of
the stator pole projects through the housing wall.

40. An electric machine according to claim 39, wherein the housing wall
resists fluid transfer between a stator portion of the electric machine
and a rotor portion of the electric machine.

41. An electric machine according to claim 39, wherein an interface
between the first portion of stator pole and the housing wall is sealed
to resist fluid transfer across the housing wall.

42. An electric machine according to claim 39, wherein:the stator pole
includes a first leg and a second leg; andeach of the first and second
legs of the stator pole project through the housing wall.

43. An electric machine according to claim 39, wherein:a second portion of
the stator pole not projecting through the housing wall has a laminar
construction having a plurality of layers; andthe first portion of the
stator pole projecting through the housing wall has a non-laminar
construction.

44. An electric machine according to claim 43, wherein the first portion
of the stator pole is coupled to the second portion of the stator pole by
at least one of a dovetail joint, a weld, or a braze.

45. An electric machine according to claim 43, further comprising one or
more slots formed in the non-laminar first portion of the stator pole
projecting through the housing, the slots configured to align with the
layers of the laminar second portion of the stator pole.

46. An electric machine according to claim 45, wherein at least one of the
slots is non-linear.

47. An electric machine according to claim 45, wherein:heat generated by
the stator boils the fluid in the housing from a liquid to a gas; andthe
electric machine further comprises a compressor configured to transfer
the gas back to liquid and return the liquid toward the stator.

48. An electric machine, comprising:a stator having a stator pole; anda
rotor including a rotor pole, the rotor configured to rotate relative to
the stator; anda plurality of slots formed in the stator or the rotor,
the plurality of slots configured to reduce eddy currents during
operation of the electric machine.

49. An electric machine according to claim 48, wherein the plurality of
slots are aligned in parallel.

50. An electric machine according to claim 48, wherein the plurality of
slots are arranged to align with multiple layers of an adjacent laminar
structure of the stator or the rotor.

51. An electric machine according to claim 48, wherein at least one of the
plurality of slots defines a curved or bent path.

52. An electric machine according to claim 48, wherein:the stator pole
includes two legs defining a gap between the two legs;the rotor pole
rotates through the gap between the two legs of the stator pole;the rotor
pole includes a laminar rotor pole structure including multiple layers;
andthe plurality of slots are formed in the two legs of the stator pole
such that they align with the layers of the laminar rotor pole structure
as the rotor pole rotates through the gap between the two legs of the
stator pole.

53. An electric machine according to claim 48, wherein:the stator pole
includes two legs defining a gap between the two legs;the rotor pole
rotates through the gap between the two legs of the stator pole; andthe
two legs of the stator pole includes a laminar structure including
multiple layers; andthe plurality of slots are formed in the rotor pole
such that they align with the layers of the laminar structure of the
stator pole legs as the rotor pole rotates through the gap between the
stator pole legs.

Description:

RELATED APPLICATION

[0001]This application claims the benefit under 35 U.S.C. § 119(e) of
U.S. Provisional Application No. 60/952,339, filed Jul. 27, 2007, The
contents of that application are incorporated herein in their entirety by
this reference.

TECHNICAL FIELD OF THE INVENTION

[0002]This invention relates in general to electric machines and, more
particularly, to short-flux path motors/generators.

BACKGROUND OF THE INVENTION

[0003]Electric machines using rotor/stator configurations (e.g., switched
reluctance motors (SRM) and permanent magnet motors (PMM)) generally
include components constructed from magnetic materials such as iron,
nickel, or cobalt. In an SRM, a pair of opposing coils in the SRM may
become electronically energized. The inner magnetic material is attracted
to the energized coil causing an inner assembly to rotate while producing
torque. Once alignment is achieved, the pair of opposing coils is
de-energized and a next pair of opposing coils is energized. In a PMM,
the inner assembly may include permanent magnets, which may provide both
push and pull forces relative to the energized coils (as opposed to only
pulling forces in an SRM).

SUMMARY OF THE INVENTION

[0004]According to certain embodiment of the present disclosure, an
electric machine includes a stator and a rotor. The stator includes a
stator pole including a first leg and a second leg, and a gap defined
between the first and second legs. The rotor includes a rotor pole. The
rotor is configured to rotate relative to the stator such that the rotor
pole rotates through the gap defined between the first and second legs of
the stator pole. The stator pole includes a laminar stator pole structure
including multiple lamination layers.

[0005]According to other embodiments of the present disclosure, an
electric machine includes a housing, a stator having a stator pole
including a first leg and a second leg, and a rotor including a rotor
pole. The rotor is configured to rotate relative to the stator. At least
one of the stator and the rotor is adjustably coupled to the housing to
allow a distance between the stator pole and the rotor pole to be
adjusted.

[0006]According to other embodiments of the present disclosure, an
electric machine includes a first stator, a first rotor, a second stator,
and a second rotor. The first stator has a first perimeter and a
plurality of first stator poles arranged around the first perimeter, each
first stator pole including a first leg and a second leg. The first rotor
is configured to rotate relative to the first stator around a first axis.
The second stator has a second perimeter and a plurality of second stator
poles arranged around the second perimeter, each second stator pole
including a first leg and a second leg. The second rotor is configured to
rotate relative to the second stator around the first axis. The second
stator is rotationally offset from the first stator about the first axis
such that the second stator poles are offset from the first stator poles.

[0007]According to other embodiments of the present disclosure, an
electric machine includes a stator and a rotor. The stator has a
plurality of stator pairs arranged around a stator perimeter, each stator
pair including two legs. The rotor has a plurality of rotor blades
arranged around a rotor perimeter, each rotor blade including two legs.
The rotor rotates relative to the stator. At least three stator pairs are
energized simultaneously to generate magnetic circuits with at least
three corresponding rotor blades.

[0008]According to other embodiments of the present disclosure, an
electric machine includes a stator and a rotor. The stator has a
plurality of stator pairs arranged around a stator perimeter, each stator
pair including two legs. The rotor has a plurality of rotor blades
arranged around a rotor perimeter, each rotor blade including two legs.
All of the plurality of stator pairs are energized simultaneously and
de-energized simultaneously, in an repeating manner, in order to cause
the rotor to rotate relative to the stator.

[0009]According to other embodiments of the present disclosure, an
electric machine includes a stator and a rotor. The stator includes a
plurality of stator pairs, each stator pair including two legs defining a
gap between the two legs. The rotor includes a plurality of rotor blades
including a permanent magnet. The rotor is configured to rotate relative
to the stator such that the rotor blade rotate through the gaps between
the two legs of each stator pair.

[0010]According to other embodiments of the present disclosure, an
electric machine includes a stator including a stator pole, a rotor
including a rotor pole and configured to rotate relative to the stator,
and a housing configured to house a fluid for cooling the stator. A first
portion of the stator pole projects through a wall in the housing.

[0011]According to other embodiments of the present disclosure, an
electric machine includes a stator having a stator pole, a rotor
including a rotor pole and configured to rotate relative to the stator,
and a plurality of slots formed in the stator or the rotor, the plurality
of slots configured to reduce eddy currents during operation of the
electric machine.

[0012]Certain embodiments of the invention may provide numerous technical
advantages. For example, a technical advantage of some embodiments may
include the capability to produce very high torque and power densities in
motors and generators. Other technical advantages of other embodiments
may include the capability to balance forces in short-flux path
motor/generators to reduce cogging, vibration, and/or noise. Other
technical advantages of other embodiments may include the capability to
efficiently remove waste heat from electrical and magnetic circuits by
evaporating or boiling a volatile fluid. Yet other technical advantages
of other embodiments may include methods for laminating stators and
rotors for increased magnetic flux and reduced eddy currents. Yet other
technical advantages of other embodiments may include methods for
increasing the area of overlap between a stator core and a rotor blade,
which may increase torque for a given magnetomotive force Ni. Yet other
technical advantages of other embodiments may include methods for
interrelating U-shaped stators and U-shaped rotors to increase torque.
Yet other technical advantages of other embodiments may include methods
for adjusting the stator poles and/or rotor poles in an axial direction
in order to adjust the area of overlap between the stator poles and rotor
poles, which may be used to control the torque output for a given
magnetomotive force Ni. Yet other technical advantages of other
embodiments may include methods for configuring and controlling a
permanent-magnet flat-blade rotor/U-shaped stator design. Yet other
technical advantages of other embodiments may include methods for
staggering stator sets to overcome noise, vibration, and/or "cogging"
effects. Yet other technical advantages of other embodiments may include
methods for cooling the electrical machine. Yet other technical
advantages of other embodiments may include methods for penetrating a
sealed housing wall with a magnetic circuit. Yet other technical
advantages of other embodiments may include methods for reducing eddy
currents in non-laminar metal, e.g., using slots. Yet other technical
advantages of other embodiments may include methods for linking "magnetic
legs" to reduce space, noise, vibration, and/or cogging effects.

[0013]Various embodiments according to the present disclosure may include
none, any one, or any combination of technical advantages discussed
above, and/or various other technical advantages not discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]To provide a more complete understanding of the embodiments of the
invention and features and advantages thereof, reference is made to the
following description, taken in conjunction with the accompanying
FIGURES, wherein like reference numerals represent like parts, in which:

[0041]FIG. 26B shows a cross-section taken along line 26B-26B in FIG. 26A
of a portion of a bundle of round wires in an example close-packed
configuration;

[0042]FIG. 27 shows a relationship between magnetic field intensity and
magnetic flux density for a 0.012-inch-thick M-5 grain-oriented
electrical steel;

[0043]FIG. 28 show the relationship between magnetic field density and
magnetic flux permeability for a 0.012-inch-thick M-5 grain-oriented
electrical steel;

[0044]FIG. 29 shows that a force f is constant with respect to the
fractional closure (x/b) of a flat bade relative to a U-shaped core,
except for high area ratios (Ago/Ac) where the core starts
to saturate;

[0045]FIG. 30 shows that the magnetic flux φ increases linearly with
the fractional closure (x/b) of a flat bade relative to a U-shaped core,
except for high area ratios (Ago/Ac) when the core starts
to saturate;

[0046]FIG. 31 shows that the core magnetic flux density Bc has a
similar pattern as the magnetic flux φ relative to the fractional
closure (x/b) of a flat bade relative to a U-shaped core;

[0047]FIG. 32 shows that the gap magnetic flux density Bg (which is
the same as the blade magnetic flux density Bb) is nearly constant
for each area ratio Ago/Ac and fractional closure (x/b) of
a flat bade relative to a U-shaped core, except when the core starts to
saturate at high area ratios;

[0048]FIG. 33 shows a representation of an alternative geometry of a
rotor/stator configuration in which a U-shaped rotor blade slides past a
U-shaped stator core;

[0049]FIG. 34 shows a representation of another alternative geometry of a
rotor/stator configuration, which is representative of a rotor moving
relative to a pair of opposite stator poles in a conventional switched
reluctance motor;

[0050]FIGS. 35A and 35B illustrate examples of how the linear motion shown
in FIGS. 26A and 33 can be converted to rotary motion;

[0051]FIGS. 36A and 36B show that the U-shaped stators in the
configurations shown in FIGS. 26A and 33 may be similar, but rotated by
90 degrees relative to each other;

[0052]FIGS. 37A and 37B show an example orientation of lamination layers
for a U-shaped blade/U-shaped core configuration and a flat
blade/U-shaped core configuration, respectively, according to certain
embodiments;

[0053]FIG. 38 shows an example orientation of lamination layers for a
stator pair and a flat blade in a flat blade/U-shaped core rotor/stator
configuration, according to certain embodiments;

[0054]FIG. 39 shows an example method of making a laminar stator by
wrapping the laminations around a mandrel, according to certain
embodiments;

[0055]FIG. 40A shows an example technique for cutting a laminar structure
at a non-right angle to for a U-shaped stator having an area ratio
Ago/Ac>1, according to certain embodiments;

[0056]FIGS. 40B and 40C show adjustment of a U-shaped stator in an axial
direction relative to a flat blade in order to adjust the gap area
Ag between the stator legs and the flat blade, which adjusts the
torque generated for a given Ni, according to certain embodiments;

[0057]FIGS. 41A and 41B show various housing aspect ratios L/r ranging
from 1.0 to 4.0, which are used in the subsequent analysis of various
rotor/stator configurations;

[0067]FIG. 51 shows a "unit cell" for a first U-shaped stator pair for use
in a U-shaped blade/U-shaped core rotor/stator configuration, and a
second U-shaped stator pair offset from the first U-shaped stator pair,
according to certain embodiments;

[0068]FIG. 52 shows the rotation of an example U-shaped blade/U-shaped
core rotor/stator configuration including double the number of rotor
blades and stator pairs as FIG. 48, according to certain embodiments;

[0070]FIG. 54 shows an example U-shaped blade/U-shaped core rotor/stator
configuration having an equal number of rotor blades and stator poles
(12/12), and where all stator poles may be energized/de-energized
simultaneously, according to certain embodiments;

[0072]FIG. 56 shows how the stator poles of a U-shaped blade/U-shaped core
rotor/stator configuration having an equal number of rotor blades and
stator poles (16/16) can all be energized at the same time, according to
certain embodiments;

[0073]FIG. 57 shows the rotation of an example flat blade/U-shaped core
rotor/stator configuration in a 6/4 configuration, according to certain
embodiments;

[0077]FIGS. 61A, 61B, and 61C show that for certain embodiments of a flat
blade/U-shaped core rotor/stator configuration, the stator width b is

b = 2 π r 8 ##EQU00002##

with a denominator of 8 for the 6/4 configuration, 16 for a 12/8
configuration, and 32 for a 24/16 configuration;

[0078]FIG. 62A shows a "unit cell" for a U-shaped stator pair for use in a
flat blade/U-shaped core rotor/stator configuration, along with a second
U-shaped stator pair of an adjacent set of stators, showing how a wire
bundle can be wrapped around the legs of adjacent stator pairs to form a
"magnetic leg," according to certain embodiments;

[0079]FIG. 62B shows mechanically coupling unit cells together to create a
series of "magnetic legs" that have a common core with the magnetic flux
flowing in the same direction, according to certain embodiments;

[0080]FIG. 63A shows a "unit cell" for a U-shaped stator pair for use in a
flat blade/U-shaped core rotor/stator configuration, which is similar to
FIG. 62A, except the width of the core body is narrowed from b to b*,
according to certain embodiments;

[0081]FIG. 63B shows an unfolded view of the unit cell of FIG. 63A,
according to certain embodiments;

[0082]FIG. 64 shows the rotation of an example permanent-magnetic
flat-blade motor including permanent magnet flat blades on the rotor,
according to certain embodiments;

[0084]FIG. 66 shows an example system and method for cooling stators that
pierce a housing wall of a cooling system housing, according to certain
embodiments;

[0085]FIG. 67 shows a configuration of a stator pole including a
non-laminar portion provided for piercing a housing wall of a cooling
system, in order to resist leakage through the housing wall, according to
certain embodiments;

[0086]FIG. 68 shows details of a non-laminar portion of a stator pole
(e.g., as used in the configuration of FIG. 67), including slots
configured to align with lamination layers of a laminar portion of the
stator pole, according to certain embodiments; and

[0087]FIG. 69 shows details of a non-laminar leg portions of a U-shaped
stator pole (e.g., as used in the configuration of FIG. 67), including
slots configured to align with both (a) lamination layers of a laminar
portion of the stator pole and (b) lamination layers or slots of a flat
rotor blade configured to pass between the U-shaped stator leg portions;
according to certain embodiments;

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0088]It should be understood at the outset that although example
implementations of embodiments of the invention are illustrated below,
embodiments of the present invention may be implemented using any number
of techniques, whether currently known or in existence. The present
invention should in no way be limited to the example implementations,
drawings, and techniques illustrated below. Additionally, the drawings
are not necessarily drawn to scale.

[0089]Various electric machines such as motors and generators and type
variations associated with such motors and generators may benefit from
one or more of the embodiments described herein. Example type variations
include, but are not limited to, switched reluctance motors (SRM),
permanent magnet AC motors, brushless DC (BLDC) motors, switched
reluctance generators (SRG), permanent magnet AC generators, and
brushless dc generators (BLDCG). Although particular embodiments are
described with reference to one or more type variations of motor and/or
generators, it should be expressly understood that such embodiments may
be utilized with other type variations of motors or generators.
Accordingly, the description provided with certain embodiments described
herein are intended only as illustrating examples type variations that
may avail benefits of embodiments of the invention. For example,
teachings of some embodiment of the invention increase the torque, power
densities, and efficiency of electric motors, particularly switched
reluctance motors (SRM) and permanent magnet AC motors (PMM). Such
embodiments may also be used with brushless DC (BLDC) motors, for
example. Some of same advantages described with reference to these
embodiments may be realized by switched reluctance generators (SRG),
permanent magnet AC generators, and brushless dc generators (BLDCG).

[0090]In conventional radial and axial SRMs, the magnetic flux flows
through a long path through the whole body of a stator and rotor. Due to
the saturation of iron, conventional SRMs have a large drop in the
magneto motive force (MMF) because the flux path is so large. One way to
reduce the loss of MMF is to design thicker stators and rotors, which
reduces the flux density. However, this approach increases the weight,
cost, and size of the machine. Accordingly, teachings of embodiment of
the invention recognize that a more desirable approach to reduce these
losses is to minimize the flux path, which is a function of geometry and
type of machine.

[0091]Teachings of some embodiments additionally introduce a new family of
stator/pole interactions and configurations for SRMs and PMMs. In this
family, stator poles have been changed from a conventional cylindrical
shape to U-shaped pole pairs. This configuration allows for a shorter
magnetic flux path, which in particular embodiments may improve the
efficiency, torque, and power density of the machine.

[0092]To take full advantage of the isolated rotor/stator structures of
this invention, sensorless SRM, PMM, and BLDC control methods may be
utilized, according to particular embodiments.

[0093]The switched reluctance motor (SRM) has salient poles on both the
stator and rotor. It has concentrated windings on the stator and no
winding on the rotor. This structure is inexpensive and rugged, which
helps SRMs to operate with high efficiency over a wide speed range.
Further, its converter is fault tolerant. SRMs can operate very well in
harsh environments, so they can be integrated with mechanical machines
(e.g., compressors, expanders, engines, and pumps). However, due to the
switching nature of their operation, SRMs need power switches and
controllers. The recent availability of inexpensive power semiconductors
and digital controllers has allowed SRMs to become a serious competitor
to conventional electric drives.

[0094]There are several SRM configurations depending on the number and
size of the rotor and stator poles. Also, as with conventional electric
machines, SRMs can be built as linear-, rotary-, and axial-flux machines.
In these configurations, the flux flows 180 electrical degrees through
the iron. Due to saturation of iron, this long path can produce a large
drop in MMF, which decreases torque density, power, and efficiency of the
machines. Increasing the size of the stator and rotor back iron can avoid
this MMF drop, but unfortunately, it increases the motor size, weight,
and cost. Using bipolar excitation of phases can shorten the flux path,
but they need a complex converter. Also, they are not applicable when
there is no overlapping in conduction of phases.

[0096]FIG. 1A shows a schematic representation of a conventional switched
reluctance motor (SRM) 100. The SRM 100 of FIG. 1A includes a stator 110
and a rotor 140. The stator 110 includes eight stationary stator poles
120 (each with its own inductor coil 120) and the inner rotor 140
includes six rotating rotor poles 150 (no coils). The components of the
SRM 100 are typically constructed from magnetic materials such as iron,
nickel, or cobalt. In particular configurations, the materials of the SRM
100 can be laminar to reduce the effect of eddy currents. At any one
time, a pair of opposing coils 130 is energized electrically. The inner
magnetic material in the rotor poles 150 of the rotor 140 are attracted
to the energized coil 130 causing the entire inner rotor 140 to rotate
while producing torque. Once alignment is achieved, the pair of opposing
coils 130 is de-energized and the next pair of opposing coils 130 is
energized. This sequential firing of coils 130 causes the rotor 140 to
rotate while producing torque. An illustration is provided with reference
to FIG. 1B.

[0097]FIG. 1B is a dot representation of the SRM 100 of FIG. 1A. The white
circles represent the stator poles 120 and the black circles represent
the rotor poles 150. Stator poles 120A, 120B are currently aligned with
rotor poles 150A, 150B. Accordingly, the coils associated with this
alignment (coils associated with stator poles 120A, 120B) can be
de-energized and another set of coils can be fired. For example, if the
coils associated with the stator poles 120C and 120D are fired, rotor
poles 150C, 150D will be attracted, rotating the rotor 140
counter-clockwise. The SRM 100 of FIG. 1 has inherent two-fold symmetry.

[0098]FIG. 2 shows a schematic representation of a long flux path through
the conventional switched reluctance motor (SRM) 100 of FIG. 1A. In the
SRM 100, magnetic fluxes must traverse 180 degree through both the stator
110 and the rotor 140--for example, through stator pole 120G, rotor pole
150G, rotor pole 150H, stator pole 120H, and inner rotor 140, itself.
Such long flux paths can lead to the creation of undesirably eddies,
which dissipate energy as heat. Additionally, due to the high flux
density, the magneto motive force (MMF) drop will be very high,
particularly if the stator 110 and rotor 140 back iron are thin.

[0099]As an example of MMF drop, FIG. 3 shows in a chart 105 the effect of
MMF drop in the torque production of a one-phase, one horsepower machine.
In FIG. 3, output torque 170 is plotted against rotor angle 160. Line 180
show torque without the effect of saturation in the rotor 140 and stator
110 back iron and line 190 shows torque with the effect of saturation in
rotor 140 and stator 110 back iron. As can be seen, the MMF drop in
torque production can be more than 6%. Accordingly, teachings of some
embodiments reduce the length of the flux path. Further details of such
embodiments will be described in greater detail below.

[0100]FIG. 4 shows a dot representation for a switched reluctance motor
(SRM) 200, according to an embodiment of the invention. The SRM 200 of
FIG. 4 may operate in a similar manner to the SRM described with
reference to FIG. 1B. However, whereas the SRM 100 of FIG. 1B fire two
coils associated with two stator pole 120 at a time, the SRM of FIG. 4
fires four coils associated with four stator poles 220 at a time. The
increased firing of such coils/stator poles 220 increases the torque.

[0101]The SRM 200 of FIG. 4 has a rotor with eight rotor poles 250 and a
stator with twelve stator poles 220. The active magnetized sets of stator
poles 220 are denoted by arrowed lines 225 and the attractive forces
through the flux linkages (e.g., between a rotor pole 250 and stator pole
220) are shown by the shorter lines 235 through a counterclockwise
progression of 40° of rotor rotation. At 45°, the
configuration would appear identical to the 0° configuration. As
can be seen with reference to these various rotor angles, as soon as a
alignment between four stator poles 220 and four rotor poles 250 occur,
four different stator poles 220 are fired to attract the rotor poles 250
to the four different stator poles 220.

[0102]The switched reluctance motor 200 in FIG. 4 has four-fold symmetry.
That is, at any one time, four stator poles 220 (the sets denoted by
arrowed lines 225) are energized, which as referenced above, is twice as
many as a conventional switched reluctance motor (e.g., SRM 100 of FIG.
1). Because twice as many stator poles 220 are energized, the torque is
doubled.

[0103]In particular embodiments, adding more symmetry will further
increase torque. For example, six-fold symmetry would increase the torque
by three times compared to a conventional switched reluctance motor. In
particular embodiments, increased symmetry may be achieved by making the
rotor as blade-like projections that rotate within a U-shaped stator, for
example, as described below with reference to the embodiments of FIGS. 5A
and 5B. In other embodiments, increased symmetry may be achieved in other
manners as described in more details below.

[0104]As used herein, the term "U-shaped" may refer to any shape defining
a pair of legs or elongated portions, or any curved or non-linear shape
defining a pair or ends generally extending in the same direction,
including, for example, generally U-shaped, V-shaped, or C-shaped, or
multi-pronged. "U-shaped" may also be referred to as "C-shaped" or
"V-shaped."

[0105]FIGS. 5A and 5B illustrate a rotor/stator configuration 300,
according to an embodiment of the invention. For purposes of
illustration, the embodiment of the rotor/stator configuration 300 of
FIGS. 5A and 5B will be described as a switched reluctance motor (SRM).
However, as briefly referenced above, in particular embodiments, the
rotor/state configuration 300 may be utilized as other types of motors.
And, in other embodiments, the rotor/state configuration 300 may be
utilized in other types of electric machines such as generators.

[0106]In the rotor/state configuration 300 of FIGS. 5A and 5B, a
blade-like rotor pole or blade 350, affixed to a rotating body 340, is
shown passing through a U-shaped electromagnet core or U-shaped stator
pole 320. In this configuration, the flux path is relatively short,
compared to conventional SRMs. For example, the magnetic flux produced by
a coil 330 fired on the U-shaped pole 320 would pass through one leg 322
of the U-shaped stator pole 320 through the blade 350 and to the other
leg 324 of the U-shaped stator pole 320 in a circular-like path. In
particular embodiments, this short path--in addition to diminishing the
long path deficiencies described above--enables increased symmetry
because the path does not traverse the center of the rotating body 340
and has little effect, if any, on other flux paths. Additionally, in
particular embodiments, the short path enables use of the center of the
rotating body 340 for other purposes. Further details of such embodiments
will be described below. Furthermore, radial loads are applied to the
rotor with this embodiment and axial loads on the rotor are balanced.
Additionally, extra radius is afforded by the blade 350, thus increasing
generated torque.

[0107]In particular embodiments, a rotor/stator configuration (e.g., the
rotor/stator configuration 300 of FIGS. 5A and 5B) can be integrated with
other features such as a gerotor compressor/expander and other
embodiments described in the following United States patents and Patent
Application Publications: Publication No. 2003/0228237; Publication No.
2003/0215345; Publication No. 2003/0106301; U.S. Pat. No. 6,336,317; and
U.S. Pat. No. 6,530,211.

Design Case Implementation

[0108]FIGS. 6-10 illustrate a rotor/stator configuration 450, according to
an embodiment of the invention. The rotor/stator configuration 450 of
FIGS. 6-10 is used with a compressor. However, as briefly referenced
above, in particular embodiments, the rotor/stator configuration 450 may
be utilized as other types of motors and other types of electric machines
such as generators. The rotor/state configuration 450 of FIGS. 6-10
includes three stacked arrays of twelve stator poles 444 and eight rotor
blades 412. The rotor/stator configuration 450 for the compressor in
FIGS. 6-10 may operate in a similar manner to the rotor/state
configuration 300 described above with reference to FIGS. 5A and 5B. FIG.
6 shows an outer rotor assembly 400 of the rotor/stator configuration
450, according to an embodiment of the invention. The outer rotor
assembly 400 in FIG. 6 includes a bearing cap 402, a bearing sleeve 404,
a port plate 406, inlet/outlet ports 408, two rotor segments 410A/410B
with rotor blades 412 mounted, a seal plate 414 to separate the dry
compression region from the lubricated gear cavity, a representation of
the outer gear 416 (internal gear), an end plate 418 with blades 412
mounted, an outer rear bearing 420, and another bearing cap 422. In this
embodiment, the outer compressor rotor serves as the rotor for the SRM.

[0109]In this embodiment, there are eight outer rotor lobes 411 with eight
blades 412 in each radial array 413 of rotor poles. In particular
embodiments, such symmetry may be necessary to minimize centrifugal
stress/deformation. In this configuration, ferromagnetic materials
utilized for the operation of the rotor/stator configuration 450 may only
be placed in the blades 412 of the radial array 413.

[0110]FIG. 7 shows an inner rotor assembly 430 of the rotor/stator
configuration 450, according to an embodiment of the invention. The inner
rotor assembly 430 of FIG. 7 includes an inner shaft 432, a stack of
three (seven lobed) inner rotors 434A/434B/434C, a spur gear 436, and an
inner rear bearing 438.

[0111]Details of operation of the inner rotor assembly 430 with respect to
the outer rotor assembly 400, according to certain embodiments of the
invention, as well as with other configuration variations are described
in further detail in one or more of the following United States patents
and/or Patent Application Publications: Publication No. 2003/0228237;
Publication No. 2003/0215345; Publication No. 2003/0106301; U.S. Pat. No.
6,336,317; and U.S. Pat. No. 6,530,211.

[0112]FIG. 8 shows a stator/compressor case 440 of the rotor/stator
configuration 450, according to an embodiment of the invention. The
stator/compressor case 440 of FIG. 8 in this embodiment includes three
stacks 442A, 442B, 442C of twelve stator poles 444, spaced at equal
angles. Although the stator poles 444 could be mounted to the case 440 in
many ways, an external coil embodiment is shown in FIG. 8. There are two
coils 446A, 446B per stator pole 444, which are mounted in sets of three
into a nonferromagnetic base plate 448, forming a bolt-in pole cartridge
450. In particular embodiments, the coils 446A, 446B may be copper coils.
In other embodiments, the coils 446A, 446B may be made of other
materials. In particular embodiments, the number of coils 446 on a given
stator pole 444 can be increased above two, thereby reducing the voltage
that must be supplied to each coil. During operation of particular
embodiments, all poles in four cartridges 450 (90° apart) may be
magnetized simultaneously. The magnetization occurs sequentially causing
the outer rotor assembly 400 of FIG. 6 to rotate.

[0113]FIG. 9 shows a cutaway view of a composite assembly 460 of a
rotor/stator configuration 450, according to an embodiment of the
invention. The composite assembly 460 shows an integration of the outer
assembly 400, the inner assembly 430, and the stator/compressor case 440
of FIGS. 6-8 as well as end plates 462 providing bearing support and gas
inlet/outlet porting through openings 464. FIG. 10 shows the composite
assembly 460 without the cutaway.

[0114]In certain embodiments, during operation, the rotor may expand due
to centrifugal and thermal effects. To prevent contact between the rotor
poles and stator poles, a large air gap is typically used. However, it is
known that the torque is strongly affected by the air gap: a smaller gap
results in more torque. Accordingly, there are advantages to reducing the
gap as small as possible. Teachings of some embodiments recognize
configurations for maintaining small gap during thermal and centrifugal
expansion of a rotor.

[0115]FIG. 11 shows a side view of how a rotor 540 changes shape when it
expands due to centrifugal and thermal effects. The rotor 540 has an axis
of rotation 503. The solid line 505 represents the rotor 540 prior to
expansion and the dotted line 507 represents the rotor 540 after
expansion. Dots 510A, 512A, and 514A represent points on the rotor 540 at
the cold/stopped position and dots 510C, 512C, and 514C represent the
same points on the rotor 540 at the hot/spinning position. The left edge
or thermal datum 530 does not change because it is held in place whereas
the right edge is free to expand. The trajectories 510B, 512B, and 514B
of dots is purely radial at the thermal datum 530 and becomes more axial
at distances farther from the thermal datum 530.

[0116]FIG. 12 shows a rotor/stator configuration 600, according to an
embodiment of the invention. The rotor/stator configuration 600 includes
a rotor 640 that rotates about an axis 603. The rotor 640 includes rotor
poles 650 that interact with stator poles 620, for example, upon firing
of coils 630. The rotor/stator configuration 600 of FIG. 12 may operate
in a similar manner to the rotor/stator configuration 300 of FIGS. 5A and
5B, except for an interface 645 between the rotor pole 650 and the stator
pole 620. In the rotor/stator configuration 600 of FIG. 12, an angle of
interface 645 between the rotor pole 650 and stator pole 620 is the same
as the trajectory of a dot on the surface of the rotor 540 shown in FIG.
11. By matching these angles, the surface of the rotor pole 650 and the
surface of the stator pole 620 slide past each other without changing an
air gap 647, even as the rotor 640 spins and heats up. This design allows
for very small air gaps to be maintained even at a wide variety of rotor
temperatures. In particular embodiments, the housing that holds the
stator pole 620 may be assumed to be maintained at a constant
temperature. Various different angles of interface 645 may be provided in
a single configuration for a rotor pole 650/stator pole 620 pair,
dependent upon the trajectory of the dot on the surface of the rotor 640.

[0117]FIGS. 13A and 13B show a rotor/stator configuration 700A, 700B,
according to another embodiment of the invention. The rotor/stator
configurations 700A, 700B include rotors 740 that rotate about an axis
703. The rotor/stator configurations 700A, 700B of FIGS. 13A and 13B may
operate in a similar manner to the rotor/stator configuration 300 of
FIGS. 5A and 5B, including rotor poles 750, stator poles 720A, 720B, and
coils 730A, 730B. The rotor/stator configuration 700A of FIG. 13A show
three U-shaped stators 720A, operating as independent units. The
rotor/stator configuration 700B of and FIG. 13B shows a single E-shaped
stators 710B operating like three integrated U-shaped stators 720A. This
E-shaped stator 720B allows for higher torque density. Although an
E-shaped stator 720B is shown in FIG. 13B, other shapes may be used in
other embodiments in integrating stator poles into a single unit.

[0118]FIG. 14 shows a rotor/stator configuration 800, according to another
embodiment of the invention. In a similar manner to that described above
with other embodiments, the rotor/stator configuration 800 of FIG. 14 may
be utilized with various types of electric machines, including motors and
generators. The rotor/stator configuration 800 of FIG. 14 may operate in
a similar manner to the rotor/stator configuration 300 of FIGS. 5A and
5B, including rotor poles 850 and U-shaped stator poles 820. However, the
stator poles 820 have been axially rotated ninety degrees such that the
rotor poles 850 do not transverse between a gap of the U-shape stator
poles 820. Similar to FIGS. 5A and 5B, the flux path is relatively short.
For example, the magnetic flux produced by a coil fired on the U-shaped
pole 820 would pass through one leg 822 of the pole 820 through the rotor
pole 850 through a periphery of the rotor through another rotor pole 850
and to the other leg 824 of the pole 820 in a circular-like path.

[0119]The rotor/stator configuration 800 of FIG. 14 is shown with three
phases A, B, and C and two pairs of stator poles 820 per each phase. In
this embodiment, stator poles 820 are U-shaped iron cores with coils that
are inserted into a non-ferromagnetic yoke 890. In other embodiments the
stator poles 820 may be made of materials other than iron and may have
other configurations. The stator poles 820 in particular embodiments may
be electrically and magnetically isolated from each other. The rotor 840
in the embodiment of FIG. 14 may operate like a rotor of a conventional
SRM; however, unlike a conventional SRM, the pitches of the rotor pole
850 and stator pole 820 are the same.

[0120]The magnetic reluctance of each phase changes with position of the
rotor 840. As shown in FIG. 15, when a rotor pole 850 is not aligned with
two stator poles 820, the phase inductance is at a minimum and this
position may be called an unaligned position. When the rotor pole 850 is
aligned with the stator pole 820, the magnetic inductance is at a maximum
and this position may be called an aligned position. Intermediate between
the aligned position and unaligned position is an intermediate position.
SRM torque is developed by the tendency of the magnetic circuit to find
the minimum reluctance (maximum inductance) configuration.

[0121]The configuration of FIG. 14 is such that whenever the rotor 840 is
aligned with one phase, the other two phases are half-way aligned, so the
rotor 840 can move in either direction depending which phase will be
excited next.

[0122]For a phase coil with current i linking flux, the co-energy W' can
be found from the definite integral:

W ' = ∫ 0 i λ i ( 1 )
##EQU00003##

The torque produced by one phase coil at any rotor position is given by:

T = [ ∂ W ' ∂ θ ] i =
constant ( 2 ) ##EQU00004##

The output torque of an SRM is the summation of torque of all phases:

T m = j = 1 N T ( i j , θ ) ( 3 )
##EQU00005##

If the saturation effect is neglected, the instantaneous torque can be
given as:

T = 1 2 i 2 L θ ( 4 ) ##EQU00006##

[0123]From Equation 4, it can be seen that to produce positive torque
(motoring torque) in SRM, the phase has to be excited when the phase bulk
inductance increases, which is the time that the rotor moves towards the
stator pole. Then it should be unexcited when it is in aligned position.
This cycle can be shown as a loop in flux linkage (λ)--phase
current (iph) plane, which is called energy conversion loop as shown
in FIG. 16. The area inside the loop (S) is equal to the converted energy
in one stroke. So the average power (Pave) and the average torque of
the machine (Tave) can be calculated as follows:

where, Np, Nr, Nph, ω are the number of stator pole
pairs per phase, number of rotor poles, number of stator phases, and
rotor speed, respectively.

[0124]By changing the number of phases, stator pole pitch, and stator
phase-to-phase distance angle, different types of short-flux-path SRMs
can be designed.

[0125]FIG. 17 shows a rotor/stator configuration 900, according to another
embodiment of the invention. The rotor/stator configuration 900 of FIG.
17 is a two-phase model, which operates in a similar manner to the model
described with reference to FIG. 14. The configuration 900 of FIG. 17
includes rotor 940; rotor poles 950; stator poles 920; legs 922, 924; and
yoke 990.

[0126]FIG. 18 shows a rotor/stator configuration 1000, according to
another embodiment of the invention. In a similar manner to that
described above with other embodiments, the rotor/stator configuration
1000 of FIG. 18 may be utilized with various types of electric machines,
including motors and generators. The rotor/stator configuration 1000 of
FIG. 18 may operate in a similar manner to rotor/stator configuration
1000 of FIG. 14, including U-shaped stator poles 1020, rotor poles 1050,
a non-ferromagnetic yoke 1080, and phases A, B, and C. However, in the
rotor/stator configuration 1000 of FIG. 18, the rotor poles 1050 are
placed radially outward from the stator poles 1020. Accordingly, the
rotor 1040 rotates about the stator poles 1020. Similar to FIG. 14, the
flux path is relatively short. For example, the magnetic flux produced by
a coil fired on the U-shaped stator pole 1020 would pass through one leg
1022 of the stator pole 1020 through the rotor pole 1050 and to the other
leg 1024 of the stator pole 820 in a circular-like path. As one example
application of the rotor/stator configuration 1000 according to a
particular embodiment, the rotor/stator configuration 1000 may be a motor
in the hub of hybrid or electric (fuel cell) vehicles, and others. In
this embodiment, the wheel is the associated with the rotor 1040,
rotating about the stators 1020. This rotor/stator configuration 1000 may
additionally be applied to permanent magnet motors, for example, as shown
in FIG. 19.

[0127]FIG. 19 shows a rotor configuration 1100, according to another
embodiment of the invention. The rotor/stator configuration 1100 of FIG.
14 may operate in a similar manner to rotor/stator configuration 1100 of
FIG. 14, including U-shaped stator poles 1120, a non-ferromagnetic yoke
1190, and phases A, B, and C, except that a rotor 1140 contains
alternating permanent magnet poles 1152, 1154.

[0128]FIG. 20 shows a rotor/stator configuration 1200, according to
another embodiment of the invention. In a similar manner to that
described above with other embodiments, the rotor/stator configuration
1200 of FIG. 20 may be utilized with various types of electric machines,
including motors and generators. The rotor/stator configuration 1200 of
FIG. 20 integrates several concepts described with reference to other
embodiments, including blades 1250A, 1250B from FIGS. 5A and 5B; E-shaped
stator poles 1220A, 1220B from FIG. 13B; stator poles 1220B radially
inward of rotor poles 1250B from FIGS. 6-10; and stator poles 1220A
radially outward of rotor poles 1250B from FIG. 18. The stator poles
1220A are rigidly mounted both on the inside and outside of a drum 1285,
which allows torque to be applied from both the inside and outside
thereby increasing the total torque and power density. In particular
embodiments, the rotor poles 1250A, 1250B may be made of a ferromagnetic
material, such as iron, which is a component of a switched reluctance
motor. In other embodiments, the rotor poles 1250A, 1250B could be
permanent magnets with the poles parallel to the axis of rotation, which
would be a component of a permanent magnet motor.

[0129]FIGS. 21A and 21B show a rotor/stator configuration 1300, according
to another embodiment of the invention. In a similar manner to that
described above with other embodiments, the rotor/stator configuration
1200 of FIGS. 21A and 21B may be utilized with various types of electric
machines, including motors and generators. The rotor/stator configuration
1300 of FIGS. 21A and 21B may operate in a similar manner to the
rotor/stator configuration 1300 of FIGS. 5A and 5B, including rotor poles
1350 and U-shaped stator poles 1320. However, the rotor poles 1350 and
U-shaped stator poles 1320 have been rotated ninety degrees such that
rotor poles 1350 rotate between a leg 1322 of the stator pole 1320 that
is radially inward of the rotor pole 1350 and a leg 1324 of the stator
pole 1320 that is radially outward of the rotor pole 1350. In the
embodiment of the rotor/stator configuration 1300 of FIGS. 21A and 21B,
it can be seen that the axial and radial fluxes co-exist.

[0130]In this embodiment and other embodiments, there may be no need for a
magnetic back-iron in the stator. Further, in this embodiment and other
embodiments, the rotor may not carry any magnetic source. Yet further, in
particular embodiments, the back iron of the rotor may not need to be
made of ferromagnetic material, thereby creating flexibility design of
the interface to the mechanical load.

[0131]In this embodiment and other embodiments, configuration may offer
higher levels of power density, a better participation of stator and the
rotor in force generation process and lower iron losses, thereby offering
a good solution for high frequency applications. In various embodiments
described herein, the number of stator and rotor poles can be selected to
tailor a desired torque versus speed characteristics. In particular
embodiments, cooling of the stator may be very easy. Further, the modular
structure of certain embodiments may offer a survivable performance in
the event of failure in one or more phases.

Optimization of the Magnetic Forces

[0132]FIGS. 22-25 illustrate an optimization of magnetic forces, according
to embodiments of the invention. The electromagnetic force on the surface
of a rotor has two components, one that is perpendicular to the direction
of motion and one that is tangent to the direction of motion. These
components of the force may be referred to as normal and tangential
components of the force and can be computed from magnetic field
quantities according to the following equations:

For an optimal operation, the tangential component of the force needs to
be optimized while the normal component of the force has to be kept at a
minimal level or possibly eliminated. This, however, is not the case in
conventional electromechanical converters. To the contrary, the normal
force forms the dominant product of the electromechanical energy
conversion process. The main reason for this can be explained by the
continuity theorem given below. As the flux lines enter from air into a
ferromagnetic material with high relative permeability the tangential and
normal components of the flux density will vary according to the
following equations:

The above equations suggest that the flux lines in the air gap will enter
the iron almost perpendicularly and then immediately change direction
once enter the iron. This in turn suggests that in a SRM and on the
surface of the rotor we only have radial forces.

[0133]FIG. 22 illustrates the formation of flux lines in a SRM drive. The
flux density, B, is shown in Teslas (T). The radial forces acting on the
right side of the rotor (also referred to as fringing flux--indicated by
arrow 1400) create radial forces (relative to the rotor surface) that
create positive propelling force for the rotor. This is the area that
needs attention. The more fluxes are pushed to this corner, the better
machine operates. This explains why SRM operates more efficient under
saturated condition. This is because due to saturation, the effective air
gap of the machine has increased and more flux lines are choosing the
fringing path.

[0134]To enhance the migration of flux lines towards the fringing area,
one embodiment of the invention uses a composite rotor surface. In the
composite rotor surface, the top most part of the of the rotor is formed
by a material that goes to saturation easier and at a lower flux density,
thereby reinforcing the fringing at an earlier stage of the
electromechanical energy conversion process. In particular embodiments,
the shape of the flux barrier or the shape of the composite can be
optimized to take full advantage of the magnetic configuration. In
another embodiment, flux barriers can be introduced in the rotor to
discriminate against radial fluxes entering the rotor normally and push
more flux lines towards the fringing area. FIGS. 23, 24 and 25 illustrate
these embodiments.

[0135]FIGS. 23 and 24 show the placement of easily saturated materials or
flux barriers 1590A, 1590B, 1590C, and 1590D under the surface of rotors
1550A, 1550B, and stators 1520A, 1520B. Example materials for easily
saturated materials or flux barriers 1590 include, but are not limited to
M-45. Example ferromagnetic materials for the rotors 1550 and stators
1520 include, but are not limited HyperCo-50. The shape, configuration,
and placement of the easily saturated materials or flux barriers may
change based on the particular configurations of the rotors and stators.

[0137]Various different rotor/stator configurations are disclosed herein.
One type of rotor/stator configuration disclosed herein may be referred
to at "U-shaped core/flat blade" rotor/stator configurations. Some
examples of the U-shaped core/flat blade configuration are shown and
discussed above with reference to FIGS. 5-13 and 20-21. In this
configuration, the cores (or stator poles) are generally U-shaped with a
pair of legs, and the blades (or rotor poles) pass through a gap defined
between the legs of the U-shaped cores. Such blades may be referred to as
"flat" blades.

[0138]Another type of rotor/stator configuration disclosed herein may be
referred to as "U-shaped blade/U-shaped core" rotor/stator
configurations. Some examples of the U-shaped blade/U-shaped core
configuration are shown and discussed above with reference to FIGS.
14-18. In this configuration, both the cores (or stator poles) and the
blades (or rotor poles) are generally U-shaped. The U-shaped cores
include a pair of legs, and the U-shaped blades include a pair of legs.
The U-shaped cores in this configuration are axially rotated 90 degrees
as compared to the U-shaped core/flat blade configuration. Thus, unlike
in the U-shaped core/flat blade configuration, the blades in the U-shaped
blade/U-shaped core configuration do not pass through a gap between the
legs of each U-shaped core. Instead, the ends of the two legs of each
U-shaped blade slide just past the ends of the two legs of each U-shaped
core, e.g., as shown in FIGS. 14, 15, 17, and 18.

[0139]Presented below are methods for calculating the theoretical torque
and other performance characteristics provided by various rotor/stator
configurations. In particular, FIGS. 26-32, along with the corresponding
text and equations below, provide theory and calculations for determining
the torque and other performance characteristics provided by various
U-shaped core/flat blade rotor/stator configurations. Similarly, FIGS.
33-41, along with the corresponding text and equations below, provide
theory and calculations for determining the torque and other performance
characteristics provided by various U-shaped core/flat blade rotor/stator
configurations.

"Flat Blade/U-Shaped Core" Rotor/Stator Configurations

[0140]FIG. 26A illustrates a magnetic circuit created in a Flat
blade/U-shaped core rotor/stator configuration when a flat blade 1700
enters a magnetized U-shaped core 1702 having an energized wire coil
1704. U-shaped core 1702 includes a first leg 1708 and a second leg 1710,
and flat blade 1700 passes through the gap defined between legs 1708 and
1710. The magnetomotive force F of the magnetic circuit is:

where [0147]Hc=magnetic field intensity in core 1702 (Aturn/m)
[0148]Hg=magnetic field intensity in the air gaps between core 1702
and flat blade 1700 (Aturn/m) [0149]Hb=magnetic field intensity in
flat blade 1700 (Aturn/m) [0150]Ic=length of core 1702 re (m)
[0151]g=length of each of the two air gaps between core 1702 and flat
blade 1700 (m) [0152]w=width of flat blade 1700 (m)The magnetic flux
density is related to the magnetic field intensity as follows:

[0155]All or portions of blade 1700 and core 1702 may be formed from any
suitable materials. In certain applications, metals with high magnetic
permeability may be preferred. As an example only, blade 1700 and/or core
1702 may be formed from 0.012-inch-thick M-5 grain-oriented electrical
steel.

[0156]Various example dimensions are shown in FIG. 26A. It should be
understood that these are example values only, and that the components
shown in FIG. 26A may be formed with any other suitable dimensions.

[0157]FIG. 27 is a graph illustrating the relationship between B and H for
an example material: 0.012-inch-thick M-5 grain-oriented electrical
steel. The magnetic permeability (μ) is the slope of the line 1720.

[0159]The magnetic flux φ is the same everywhere in the circuit and
follows:

φ=BcAc=BgAg=BbAb (13)

where [0160]φ=magnetic flux (Wb) [0161]Ac=cross-sectional area
of core 1702 (m2), as indicated at leg 1710 in FIG. 26A
[0162]Ag=area of the air gap (i.e., the area of overlap) between
core 1702 and flat blade 1700 at an instant of time (m2)
[0163]Ab=area of flat blade 1700 through which the magnetic flux
passes at an instant of time (m2)

[0164]If the flat blade width w is small, the magnetic field lines do not
have enough space to spread out so the magnetic flux density of the air
gap and flat blade 1700 are about the same, thus allowing the following
approximation to be made:

Ab≈Ag (14)

Using this relationship, the magnetic flux density can be calculated in
each portion of the magnetic circuit.

B c = φ A c B g = φ A g B b =
φ A b ( 15 ) ##EQU00011##

Substituting the relationships in Equations 15 into Equation 12 gives the
following:

where [0165]Wfld=work required to supply energy to the magnetic
field (J) [0166]L(x)=instantaneous inductance (Wbturn/A), which is a
function of the position x of blade 1700 relative to core 1702 as blade
1700 moves through the gap between legs 1708 and 1710 (i.e., the length
of overlap between blade 1700 and core 1702), indicated as distance "x"
in FIG. 26A.As the flat blade moves laterally through the air gap between
legs 1708 and 1710 of core 1702, the inductance of the circuit increases,
thus allowing the magnetic flux to increase. The inductance is:

The instantaneous air gap Ag, which is the instantaneous area of
overlap between blade 1700 and core 1702 as blade 1700 moves through the
gap between legs 1708 and 1710, is:

A g = x b A g o ( 24 ) ##EQU00019##

where [0167]Ago=area of the closed air gap (i.e., at a
position of maximum overlap between blade 1700 and core 1702) (m2)
[0168]b=width of flat blade 1700 (m) [0169]x=position of flat blade 1700
relative to core 1702 as blade 1700 moves through the gap between legs
1708 and 1710 (i.e., the length of overlap between blade 1700 and core
1702), indicated as distance "x" in FIG. 26A (m).Equation 24 may be
substituted into Equation 23 to provide:

[0170]Equation 31 indicates that as long as core 1702 is not saturated,
the force acting on flat blade 1700 will be constant and independent of
the position x of flat blade 1700. Further, for a given core area Ac
and magnetomotive force Ni, the force increases with a smaller gap g,
increases with larger close air gap area Ago, and decreases
with greater flat blade width b.

[0171]Using the following procedure, the equations above allow the
calculation of the force in a flat blade, allowing for saturation of the
core:

[0181]FIG. 29 is a graph illustrating force f versus the fractional
closure (x/b) of the flat blade, for three different area ratios
Ago/Ac in an example Flat blade/U-shaped core stator/rotor
configuration. The parameters x, b, Ago, and Ac are
defined above with reference to FIG. 26A. x/b is the fractional closure,
or overlap, of the flat blade as the flat blade moves through the gap
between the two legs of the U-shaped core. Ago/Ac is the
ratio of the surface area of the end of a stator leg that interfaces with
the flat blade to the cross-section of that stator leg, as shown in FIG.
26A.

[0182]As shown in FIG. 29, the force f is constant with respect to the
fractional closure (x/b) of the flat blade, except for relatively high
area ratios Ago/Ac (e.g., area ratio=3) when the core
starts to saturate. A relatively high area ratio Ago/Ac
may be defined as an area ratio Ago/Ac where saturation
may have a significant effect on the force as the fractional closure
(x/b) increases, e.g., area ratio=3, as shown in FIG. 29.

[0183]FIG. 30 is a graph illustrating magnetic flux φ versus the
fractional closure (x/b) of the flat blade, for three different area
ratios Ago/Ac in an example Flat blade/U-shaped core
stator/rotor configuration. The graph indicates that the magnetic flux
φ increases linearly with fractional closure, except for relatively
high area ratios Ago/Ac (e.g., area ratio=3) when the core
starts to saturate.

[0184]FIG. 31 is a graph illustrating magnetic flux density Bc versus
the fractional closure (x/b) of the flat blade, for three different area
ratios Ago/Ac in an example Flat blade/U-shaped core
stator/rotor configuration. The graph indicates that the core magnetic
flux density Bc has a similar pattern as φ, which is expected
because the two quantities are related by the core area Ac, which is
constant.

[0185]FIG. 32 is a graph illustrating magnetic flux density in both the
blade and in the gap, Bg and Bb, versus the fractional closure
(x/b) of the flat blade, for three different area ratios
Ago/Ac in an example Flat blade/U-shaped core stator/rotor
configuration. The graph indicates that the gap and blade magnetic flux
density Bg and Bb are nearly constant for each area ratio
Ago/Ac and fractional closure, except for relatively high
area ratios Ago/Ac (e.g., area ratio=3) when the core
starts to saturate.

[0186]The graphs shown in FIGS. 29-32 were generated based on an example
Flat blade/U-shaped core stator/rotor configuration. The illustrated data
corresponding to the area ratios of 1, 2, and 3 corresponds to that
example configuration. Different configurations (e.g., different
geometries, dimensions, materials, coil turns (N), current, etc.) will
yield different results for similar area ratios. Thus, what is a
"relatively high area ratio" (i.e., where saturation has a significant
effect on the force and/or flux densities) depends on the particular
configuration. For example, an area ratio of 3 may not be affected by
saturation--and thus not a "relatively high area ratio"--in other
configurations.

[0187]In some embodiments, for a torque-dense electric motor, the core
should saturate (i.e., maximum B) just as the air gap is fully closed by
the blade (i.e., when x/b=1). This strategy may take maximum advantage of
the flux carrying capacity of the core. As shown in FIG. 31, only an area
ratio of 3 caused the core to saturate with the Ni used in that
configuration (500 Aturns). With all other parameters held constant, the
core of the smaller area ratios (1 and 2) can be saturated by increasing
Ni; however, this comes at the expense of an increased wire bundle area.
An advantage of using an increased area ratio is that it can cause
saturation of the core with a small Ni, and hence increase the force
acting on the blade. This increased force with a small Ni must come from
somewhere--it comes from an increase in voltage that delivers the
current. Thus, when the area ratio increases, it allows for a smaller Ni,
and a larger voltage.

[0188]To maximize the torque from an electric motor, the core should
saturate near x/b=1 (full closure of the air gap between the blade and
core). For the condition of saturation at closure (x/b=1):

φmax=Bc,maxAc (32)

The maximum magnetic flux occurs with the maximum allowable magnetomotive
force (Ni)max. From Equation 16 for a flat blade:

In this example, the reluctance of the blade is small, the reluctance of
the air gap is large, and the reluctance of the core is significant. It
should be understood that these values are examples only, and that any
other suitable values may be used.Equation 34 may be reformulated as:

The power density of a motor is determined by its average torque and
speed. The analysis presented above describes the torque ability of a
motor. The volumetric torque density can be calculated as follows:

[0195]FIG. 26B is a cross-sectional view of round wires 1730 of coil 1704
in a close-packed wire coil configuration, taken along line 26B-26B shown
in FIG. 26A. The packing factor P for individual wires 1730 of
cross-sectional area Ai is related to the cross-sectional area of
the wire bundle forming the coil, Aw, as follows:

P = A i A w = 1 2 π r w 2 3 r w 2
= π 2 3 = 0.907 ( 40 ) ##EQU00035##

The number of turns in a wire bundle is:

N = P A w A i ( 41 ) ##EQU00036##

An individual wire of cross-sectional area Ai has a maximum current
capacity imax, which is determined by the electrical conductivity,
the heat transfer coefficient, and the allowable temperature rise.

[0197]Various example dimensions are shown in FIG. 33. It should be
understood that these are example values only, and that the components
shown in FIG. 33 may be formed with any other suitable dimensions.

[0198]FIG. 34 illustrates a rotor/stator configuration 1830 that is
representative of a conventional switched reluctance motor (e.g., as
shown in FIGS. 1-2). The configuration includes a U-shaped core (stator)
1832 including first and second legs 1840 and 1842, and a blade (rotor)
1834. In this model, the U-shaped core 1832 represents one half of the
stator assembly shown in FIGS. 1-2. Thus, core legs 1840 and 1842
represent opposite stator poles that are simultaneously charged, e.g.,
stator poles 120G and 120H shown in FIG. 2. Blade 1834 represents rotor
140 shown in FIGS. 1-2, including rotor poles 150G and 150H. The rotation
of rotor 140 relative to stator poles 120G and 120H in FIGS. 1-2 may be
modeled as linear translation (as indicated by arrow "x" in FIG. 34), as
the movement by rotor poles 150G and 150H by stator poles 120G and 120H
may be approximated as linear translation.

[0199]Various example dimensions are shown in FIG. 34. It should be
understood that these are example values only, and that the components
shown in FIG. 34 may be formed with any other suitable dimensions.

[0200]The analysis of the geometries shown in FIGS. 33 and 34 is very
similar to the analysis presented above for the Flat blade/U-shaped core
rotor/stator configuration shown in FIG. 26A, except that the flux path
through the blades in the configurations of FIGS. 33 and 34 is much
longer than in the flat blade configuration of FIG. 26A. In particular,
in the U-shaped blade/U-shaped core configuration shown in FIG. 33, the
flux path must flow along the complete U-shaped length of the blade. And
in the conventional SRM configuration shown in FIG. 34, the flux path
must flow across the full length of the rotor (from rotor pole to
opposite rotor pole) and around one half of the stator yoke, as shown in
FIG. 2.

[0201]As a consequence of this increased flux path distance in the
configurations of FIGS. 33 and 34, the field lines have the opportunity
to spread out over the entire width of the blades, which affects its
reluctance. Also, in such configurations, the cross-sectional area of the
core, closed air gap, and blades are typically the same, as shown in
FIGS. 33 and 34.

Ac=Ago=Ab (45)

The inductance of the magnetic circuit in such configurations is as
follows:

In certain embodiments, to maximize the torque from an electric motor, the
core should saturate near x/c=1 (full closure of the air gap between the
blade and the core). For the condition of saturation at closure (x/c=1):

[0203]FIGS. 35A and 35B illustrate two examples of how the linear motion
described in FIGS. 26A and 33 can be converted to rotary motion. FIG. 35A
illustrates a U-shaped blade/U-shaped core rotor/stator configuration
1850 including a U-shaped blade 1852 positioned on a rotor that rotates
relative to a U-shaped stator 1854. The U-shaped blade 1852 includes a
pair of legs 1855 and 1856, and the U-shaped core 1854 includes a pair of
legs 1857 and 1858. The core is charged (indicated at "Start On") when
the blade legs 1855 and 1856 approach the core legs 1857 and 1858, and
turned off (indicated at "End On") when the blade legs 1855 and 1856 are
aligned with the core legs 1857 and 1858.

[0204]FIG. 35B illustrates a flat blade/U-shaped core rotor/stator
configuration 1860 including a flat blade 1862 positioned on a rotor that
rotates relative to a U-shaped core 1864. Flat blade 1862 passes between
two legs of U-shaped core 1864, e.g., as shown in FIGS. 5-13 and 26A.
Core 1864 is charged (indicated at "Start On") when blade 1862 is at some
predefined angular orientation relative to core 1864, and turned off
(indicated at "End On") when blade 1862 is aligned with core 1864.

[0205]FIGS. 36A and 36B illustrate the orientation of the U-shaped cores,
or stators, in the configurations of FIGS. 33 and 26A, respectively. The
geometries are generally similar, except rotated relative to each other
by 90 degrees. In particular, FIG. 36A illustrates a U-shaped core 1880
of the U-shaped blade/U-shaped core configuration of FIG. 33, wherein a
U-shaped blade passes by the two ends of U-shaped core 1880, but not
between the two legs of U-shaped core 1880. In contrast, FIG. 36B
illustrates a U-shaped core 1890 of the flat blade/U-shaped core
configuration of FIG. 26A, wherein a flat blade passes through legs 1892
and 1894 of U-shaped core 1890.

Laminations of Stator and/or Rotor Components

[0206]In some embodiments, all or certain portions of the stator and/or
rotor may be formed in a laminar manner, which may act to channel the
magnetic flux in the direction of the laminar layers, thus reducing
undesirable eddy currents.

[0207]FIGS. 37A and 37B illustrate example orientations for laminating
blade and core components for various rotor/stator configurations
disclosed herein, according to certain embodiments. FIG. 37A illustrates
a U-shaped blade/U-shaped core configuration including a U-shaped blade
1900 including first and second legs 1902 and 1904, and a U-shaped core
1910 including first and second legs 1912 and 1914. Each of blade legs
1902 and 1904 and core legs 1912 and 1914 may be formed with laminations
aligned in parallel planes. Although FIG. 37A shows two lamination layers
A and B, it should be understood that any suitable number of layers may
be used. FIG. 37A also illustrates magnetic flux lines 1920 flowing
between lamination layer A of stator leg 1912 and rotor leg 1902, and
between lamination layer A of stator leg 1914 and rotor leg 1904.

[0208]FIG. 37B illustrates a flat blade/U-shaped core configuration
including a flat blade 1930 and a U-shaped core 1934 including first and
second legs 1936 and 1938. As discussed above, in such configurations the
flat blade 1930 passes in the direction of the arrow through the gap
defined between first and second legs 1936 and 1938 of U-shaped core
1934. Blade 1930 and core legs 1936 and 1938 may be formed with
laminations aligned as shown in FIG. 37B. Although FIG. 37B shows two
lamination layers A and B, it should be understood that any suitable
number of layers may be used. FIG. 37B also illustrates magnetic flux
lines 1940 in lamination layer A flowing between stator legs 1936 and
1938 through blade 1930.

[0209]FIG. 38 illustrates an example orientation for laminating blade and
core components for a flat blade/U-shaped core rotor/stator
configuration, according to certain embodiments. FIG. 38 is generally
similar to FIG. 37B, but shows the full U-shaped core, the rotor to which
the flat blade is connected, and additional lamination layers. As shown
in FIG. 38, a flat blade 1950 connected to a rotor 1952, and a U-shaped
core 1954 may include multiple lamination layers aligned in a similar
manner as shown in FIG. 37B.

[0210]In this example, flat blade 1950 has a laminar structure in which
the layers are generally formed in planes perpendicular to a plane about
which rotor 1952 rotates (i.e., a plane defined by a pattern traced by a
point on flat blade 1950 as rotor 1952 rotates). Also, U-shaped core 1954
has a laminar structure that generally bends around the U-shaped length
of the core. In this example, the laminar structure turns inward toward
the end portion of each stator leg. Thus, with such configuration, the
lamination layers of flat blade 1950 are aligned generally parallel with
the lamination layers exposed at the ends of the two stator legs when
flat blade 1950 passes between the stator legs. Thus, the magnetic flux
may be channeled through flat blade 1950 from one stator leg to the
other, and eddy currents may be reduced.

[0211]In this example, flat blade 1950 and U-shaped core 1954 each include
five lamination layers. Again, it should be understood that any suitable
number of layers may be used.

[0212]FIGS. 39 and 40A-40C illustrate an example technique for forming and
utilizing a laminar U-shaped stator 1960 having an area ratio
Ago/Ac>1, according to certain embodiments. FIG. 39
illustrates a laminar material 1970 being wrapped around a mandrel 1972.
Mandrel 1972 may have one or more angled portions 1974, which facilitate
the formation of a U-shaped stator 1960 having an area ratio
Ago/Ac>1, as discussed below.

[0213]The laminar material 1970 may be wrapped around mandrel 1972 any
desired number of times to form any desired number of lamination layers.
For example, as shown in FIG. 40A, laminar material 1970 may be wrapped
around mandrel 1972 to form three layers. The layered structure may then
be cut to define the two stator legs 1980 and 1982 and the gap between
the stator legs 1980 and 1982. For example, the layered structure may
then be cut along lines 1984 and 1986, and the remaining portion 1988 may
be removed. In some embodiments, e.g., as shown in FIG. 40A, the layered
structure may be cut at a non-right angle in order to create an exposed
area Ago that is larger than the cross-sectional area Ac
of the stator legs. In this manner, U-shaped stator 1960 having an area
ratio Ago/Ac>1 may be formed.

[0214]FIGS. 40B and 40C illustrate the laminar U-shaped stator pair 1960
in use in a flat blade/U-shaped core rotor/stator configuration including
a laminar flat blade 1990 configured to pass between legs 1980 and 1982
of U-shaped stator pair 1960, and a pair of wire coils 1992 wrapped
around stator pair 1960. U-shaped stator pair 1960 may be axially
adjusted toward or away from blade 1990 (e.g., toward or away from a
center point about which the rotor rotates) in order to adjust a distance
between a point on stator pair 1960 and a point on rotor blade 1990. By
adjusting the distance between stator pair 1960 and rotor blade 1990, the
maximum area of overlap between stator pair 1960 and blade 1990 (e.g.,
during full closure) may be controlled. U-shaped stator pair 1960 may be
adjusted in any suitable manner, e.g., using a screw 1994 connected to a
stator yoke or support structure 1996, or any other suitable adjustment
mechanism.

[0215]In alternative embodiments, the position of rotor blade 1990 may be
axially adjusted toward or away from stator pair 1960 (e.g., toward or
away from a center point about which the rotor rotates) in order to
adjust a distance between a point on stator pair 1960 and a point on
rotor blade 1990. In such embodiments, rotor blade 1990 may be adjusted
in any suitable manner, e.g., using a screw connected to a rotor yoke or
support structure, or any other suitable adjustment mechanism.

[0216]In other embodiments, the positions of both stator pair 1960 and
rotor blade 1990 may be independently adjusted.

[0217]FIG. 40B shows U-shaped stator pair 1960 adjusted such that blade
1990 fully overlaps with the exposed area of stator legs 1980 and 1982,
which maximizes Ag, This configuration may allow for the maximum
flux density in core 1960, which maximizes the torque for a given Ni.
FIG. 40C shows U-shaped stator pair 1960 adjusted outward in the radial
direction (e.g., using screw 1994), which reduces Ag and reduces the
torque for a given Ni. In this manner, the position of each U-shaped
stator pair 1960 in the motor may be mechanically adjusted to alter the
torque output of the electric motor for a given Ni, as desired.

[0218]FIG. 41 illustrates two different rotor/stator motor housings 2000
and 2002 having housing aspect ratios L/r of 1.0 and 4.0, respectively.
Housing aspect ratios L/r ranging from 1.0 to 4.0 are used in the
analysis presented below. The following example dimensions are used to
illustrate these aspect ratios:

[0219]r=0.50 m

[0220]r0=varies as required

[0221]L=0.50 m

[0222]L=2.0 m

Analysis of Various Rotor/Stator Configuration Options

[0223]Various rotor/stator configuration options are analyzed and compared
below. In particular, the torque density and power density generated by
various rotor/stator configuration options are calculated and compared as
described below.

[0224]FIG. 42 illustrates a traditional 6/4 switched reluctance motor 2100
including a stator 2101 with six stator poles 2102 and a rotor 2110 with
four rotor poles 2112. Opposite stator pole pairs are energized
sequentially (currently energized stator poles are indicated with dark
shading) and the rotor 2110 completes the magnetic circuit. As magnetic
flux increases in the magnetic circuit, rotary torque is produced that
drives rotor 2130. FIG. 42 illustrates eight positions of rotor 2110 at
15 degree increments to show the rotation of rotor 2110.

[0225]FIG. 43 corresponds to FIG. 42 and illustrates the sequence that
each of the three stator pairs 1-3 is fired throughout the 360 degree
rotation of rotor 2110. Each stator pair is on for 2/6 of the time
(θon=0.3333), and there are three stator pairs
(npairs=3). One drawback to the traditional SRM is that only one
pair of stators can be energized at any given time.

[0226]FIG. 44 illustrates a traditional 12/10 switched reluctance motor
2120 including a stator 2121 with 12 stator poles 2122 and a rotor 2130
with 10 rotor poles 2132. As with the 6/4 motor 2100, opposite stator
pole pairs in the 12/10 motor are energized sequentially (currently
energized stator poles are indicated with dark shading) and rotor 2130
completes the magnetic circuit. As magnetic flux increases in the
magnetic circuit, rotary torque is produced that drives rotor 2130. FIG.
44 illustrates eight positions of rotor 2130 at 15 degree increments to
show the rotation of rotor 2130.

[0227]FIG. 45 corresponds to FIG. 44 and illustrates the sequence that
each of the six stator pairs 1-6 is fired throughout the 360 degree
rotation of rotor 2130. Each stator pair is on for 1/6 of the time
(θon=0.166667) and there are six stator pairs (npairs=6).
Notice that in general, the product θon npairs=1.

[0228]FIG. 46 illustrates a geometry of a 6/4 switched reluctance motor.
As shown, for a 6/4 switched reluctance motor, the rotor and stator width
c may be defined as:

c = 2 π r 12 ( 62 ) ##EQU00056##

For 12/10 and 24/22 switched reluctance motors, the denominators are 24
and 48, respectively (instead of 12).

[0229]FIG. 47 illustrates a "unit cell" for a stator pair of a standard
switched reluctance motor (e.g., as shown in FIGS. 1-2, 42, and 44). As
used herein, a "unit cell" is the minimum geometry that includes the
features of a stator pair for generating a magnetic circuit. For example,
in a standard SRM configuration (i.e., a long-flux configuration), a
"unit cell" includes a pair of stator poles on opposite sides of the
rotor, as well as the wire bundles (coils) for energizing the pair of
stator poles. In contrast, as discussed below, for short-flux
configurations including U-shaped stator pairs, a "unit cell" includes a
single U-shaped stator pair, along with the wire bundles (coils) for
energizing the U-shaped stator pair. The "unit cell" allows for a fair
comparison of different rotor/stator configuration options.

[0230]As shown in FIG. 47, the "unit cell" for the standard SRM
configuration includes a pair of opposite stator poles 2150A and 2150B
including the wire bundles (coils) 2152A and 2152B needed to provide the
magnetomotive force. FIG. 47 also indicates one-half of the circular
stator yoke 2154 (in dashed lines) to provide context for the stator
pair. The semi-circular half yoke is not part of the unit cell.

[0231]The area of the core Ac relative to the surface area of the
rotor Ar at radius r follows:

The length of a unit cell is the same as the overall length of the motor:

L*=L (69)

FIG. 47 shows that length e:

e=L*-2(0.5c) (70)

Rotor/Stator Configuration Option B1: U-Shaped Blade/U-Shaped Core

[0234]FIG. 48 illustrates rotor/stator configuration Option B1, which is a
U-shaped blade/U-shaped core configuration, according to certain
embodiments. The illustrated example is a 12/8 configuration, analogous
to a standard 6/4 switched reluctance motor. The rotor/stator
configuration 2200 includes a stator 2202 with six U-shaped stator pairs
1-6 and a rotor 2206 with four U-shaped blades 2208. Opposite stator
pairs 1-6 are energized sequentially (currently energized stators are
indicated with dark shading) and the relevant U-shaped blades 2208
complete the magnetic circuits. FIG. 48 illustrates eight positions of
rotor 2206 at 15 degree increments to show the rotation of rotor 2206. In
some embodiments, each U-shaped stator pair 1-6 is turned on (i.e.,
energized) when there is a slight overlap between (a) the leading corners
of the two legs of the U-shaped rotor blade 2208 coming into alignment
with that particular stator and (b) the two legs of the particular
stator. These areas of overlap between stator pair 1 and the approaching
U-shaped rotor blade 2208 are indicated in FIG. 48 at 2210.

[0235]FIG. 49 corresponds to FIG. 48 and illustrates the sequence that
each of the six U-shaped stator pairs 1-6 is fired throughout the 360
degree rotation of rotor 2206. Each stator pair is on for 1/6 of the time
(θon=0.16666), and there are six stator pairs (npairs=6).
As shown in FIG. 49, during every other interval, none of the stator
pairs are firing.

[0236]FIG. 50 illustrates a geometry of a 12/8 U-shaped blade/U-shaped
core configuration, e.g., as shown in FIG. 48. In such configuration, the
rotor and stator width c may be defined as:

c = 2 π r 24 ( 71 ) ##EQU00063##

[0237]FIG. 51 illustrates a "unit cell" for a U-shaped stator pair 2300
for use in a U-shaped blade/U-shaped core rotor/stator configuration,
e.g., as shown in FIG. 48. The unit cell includes the wire bundle (coil)
needed to provide the magnetomotive force. The area of the core Ac
relative to the surface area of the rotor Ar at radius r follows:

The parameter e depends upon the length and the number of stator sets
provided along the axis indicated by arrow A.

[0240]As discussed above, FIG. 49 indicates that half the time, no torque
is applied to the rotor, which in some embodiments or applications may
cause the rotor to "cog." Thus, multiple staggered stator sets may be
provided to eliminate the periods of no-torque. For example, as shown in
FIG. 51, a first set of U-shaped stators (extending around a perimeter of
the motor) including U-shaped stator 2300 may be complemented by a second
set of U-shaped stators including U-shaped stator 2310 offset
rotationally offset from the first set of U-shaped stators about the
first axis of rotation of the rotor. The second stator set may be
rotationally offset from the first stator set by any suitable degree. For
example, where the first stators are arranged around a perimeter at
intervals of x degrees, the second stator set may be rotationally offset
from the first stator set about the axis of rotation by x/2 degrees.
Similarly, where three stator sets are used, each second stator set may
be rotationally offset from each other by x/3 degrees. And so on. It
should be understood that these are only example configurations, and any
suitable number of stator sets and degree offset of each stator set may
be used according to the application and desired performance.

[0241]In the example configuration shown in FIG. 51 including two
staggered stator sets, the motor length must be divided into two parts;
i.e.

[0242]FIG. 52 illustrates rotor/stator configuration Option B2, which is a
U-shaped blade/U-shaped core configuration, according to certain
embodiments. Option B2 is similar to the 12/8 configuration of Option B1,
but with double the number of rotor blades and stator pairs as Option B1.
The rotor/stator configuration 2400 of FIG. 52 includes a stator 2402
with 12 U-shaped stator pairs 1-12 and a rotor 2406 with eight U-shaped
blades 2408.

[0243]In the example embodiment shown in FIG. 52, each U-shaped stator
pair shares one of its stator legs with the adjacent U-shaped stator pair
to the right, and shares its other stator leg with the adjacent U-shaped
stator pair to the left. Thus, each of the 12 stator legs of stator 2402
is shared by two U-shaped stator pairs. A wire coil may be formed around
each of the 12 stator legs. The wire coil around each leg may be used for
energizing each of the two U-shaped stator pairs that shares that leg.
For example, the around the leg shared by U-shaped stator pairs 2 and 3
shown in FIG. 52 includes a wire coil that may be energized (a) along
with the coil on adjacent stator leg to the left in order to energize
U-shaped stator pair 2 (as shown in the snapshot at 345 degrees
rotation), and (a) along with the coil on the adjacent stator leg to the
right in order to energize U-shaped stator pair 3 (as shown in the
snapshot at 15 degrees rotation).

[0244]Opposite stator pairs 1-12 are energized sequentially (currently
energized stators are indicated with dark shading) and the relevant
U-shaped blades 2408 complete the magnetic circuits. The configuration of
FIG. 52 generally allows more stator pairs to be energized at a given
time, as compared with certain other configurations. For example, while
some other configurations are limited to two stator pairs being energized
at a time, the configuration of FIG. 52 allows more than two stator pairs
to be energized at a time. In an example operation of the configuration
of FIG. 52, two groups or opposite stator pairs (i.e., a total of four
U-shaped stators) may be energized at a time, as opposed to one pair of
opposite stator pairs (i.e., a total of two U-shaped stators) energized
at a time in Option B1. FIG. 52 illustrates eight positions of rotor 2406
at 15 degree increments to show the rotation of rotor 2406.

[0245]FIG. 53 corresponds to FIG. 52 and illustrates the sequence that
each of the 12 U-shaped stator pairs 1-12 is fired throughout the 360
degree rotation of rotor 2406. Each stator pair is on for 1/3 of the time
(θon=0.33333) and that there are 12 stator pairs
(npairs=12). As shown in FIG. 53, four of the stator pairs are
firing at any given time; there are no time periods during which none of
the stator pairs are firing (as compared to Option B1).

[0246]Because the geometry of Option B2 is similar to that of Option B1
(but with double the number of rotors and stators), the rotor and stator
width c for Option B2 may be defined with reference to FIG. 50 as:

c = 2 π r 24 ( 80 ) ##EQU00070##

If the number of stator pairs is halved to six, then the denominator is
12. If number of stator pairs is doubled to 24, then the denominator is
48.

[0247]As shown in FIG. 53, there are no gaps in torque, so there is no
need to double the number of stators along the length; therefore,

[0249]FIG. 54 illustrates rotor/stator configuration Option B3, according
to certain embodiments. Option B3 is similar to Option B2, except the
number of rotor blades and stator poles is identical (e.g., 12/12 in the
example illustrated embodiment). The rotor/stator configuration 2500 of
FIG. 54 includes a stator 2502 with 12 U-shaped stator pairs 1-12 and a
rotor 2506 with 12 U-shaped blades 2508. All stator pairs 1-12 are
energized and de-energized simultaneously (the energized state is
indicated with dark shading) to complete 12 magnetic circuits with the 12
U-shaped blades 2508 (each circuit includes one U-shaped stator and one
U-shaped blade). FIG. 54 illustrates four positions of rotor 2506 at 15
degree increments to show the rotation of rotor 2506.

[0250]FIG. 55 corresponds to FIG. 54 and illustrates the sequence that
each of the 12 U-shaped stator pairs 1-12 is fired throughout the 360
degree rotation of rotor 2506. Each stator pair 1-12 is on for 1/2 of the
time (θon=0.5) and that there are 12 stator pairs
(npairs=12).

[0251]FIG. 56 illustrates another example rotor/stator configuration 2526
of Option B3, according to certain embodiments. Configuration 2526 is
similar to configuration 2520 shown in FIG. 54, except configuration 2526
is a 16/16 configuration (rather than a 12/12 configuration). FIG. 56
illustrates the arrangement of the 16 U-shaped stator pairs such that the
all 16 stator pairs can be energized at the same time. Each U-shaped
stator pair forms a magnetic circuit with a corresponding U-shaped blade
2528. The flux paths for each of the 16 magnetic circuits are indicated
at 2530.

[0252]Referring back to the 12/12 configuration shown in FIG. 54, the
rotor and stator width c for Option B2 may be defined with reference to
FIG. 50 as:

c = 2 π r 24 ( 82 ) ##EQU00071##

If the number of stator pairs is halved to six, then the denominator is
12. If number of stator pairs is doubled to 24, then the denominator is
48. If number of stator pairs is 16 (e.g., the configuration shown in
FIG. 56), then the denominator is 32.

[0253]As shown in FIG. 55, there are gaps in torque in the Option B3
configurations, and thus for modeling the system, two stators are present
along the length L, as compared to one in Option B1; therefore,

L*=1/2L (83)

[0254]The other formulas are identical to Option B1.

Rotor/Stator Configuration Option C1: Flat Blade/U-Shaped Core

[0255]FIG. 57 illustrates rotor/stator configuration Option C1, which is a
flat blade/U-shaped core configuration, according to certain embodiments.
The illustrated example is a 6/4 configuration. The rotor/stator
configuration 2600 includes six U-shaped stator pairs 1-6 and a rotor
2606 with four flat blades 2608. Each U-shaped stator pair includes two
legs, and the flat rotor blades 2608 pass through the gap formed between
the stator legs, e.g., as shown and discussed above regarding FIGS. 5-13
and 26A. Opposite stator pairs 1-6 are energized sequentially (currently
energized stators are indicated with dark shading) and the relevant flat
blades 2608 complete the magnetic circuits.

[0256]FIG. 57 illustrates eight positions of rotor 2606 at 11.25 degree
increments to show the rotation of rotor 2606. In some embodiments, each
U-shaped stator pair 1-6 is turned on (i.e., energized) when there is a
slight overlap between (a) the leading edge of a flat rotor blade 2608
coming into alignment with that particular stator and (b) the two legs of
the particular stator. In some embodiments, each U-shaped stator pair 1-6
is turned off (i.e., de-energized) when the flat blade 2608 is fully
aligned between the two legs of the stator (i.e., full closure). As
shown, one or two sets of stator pairs 1-6 (i.e., a total of two or four
U-shaped stators) are energized at any given time.

[0257]FIG. 58 corresponds to FIG. 57 and illustrates the sequence that
each of stator pairs 1-6 is energized throughout the 360 degree rotation
of rotor 2606. As shown, one or two sets of stator pairs 1-6 (i.e., a
total of 2 or 4 U-shaped stators) are energized at any given time. Each
stator pair is on for 4/9 of the time (θon=0.444) and that
there are six stator pairs (npairs=6). Notice that there is overlap
as the pairs are fired, which will lead to smooth rotation.

[0258]FIG. 59 illustrates another example rotor/stator configuration of
Option C1, according to certain embodiments. This example includes a 12/8
configuration 2620 including 12 U-shaped stator pairs 1-12 and a rotor
2626 with eight flat blades 2628. Each U-shaped stator pair includes two
legs, and the flat rotor blades 2628 pass through the gap formed between
the stator legs, e.g., as shown and discussed above regarding FIGS. 5-13
and 26A. Opposite stator pairs 1-12 are energized sequentially (currently
energized stators are indicated with dark shading) and the relevant flat
blades 2628 complete the magnetic circuits.

[0259]FIG. 59 illustrates eight positions of rotor 2626 at 5.625 degree
increments to show the rotation of rotor 2626. In some embodiments, each
U-shaped stator pair 1-12 is turned on (i.e., energized) when there is a
slight overlap between (a) the leading edge of a flat rotor blade 2628
coming into alignment with that particular stator and (b) the two legs of
the particular stator. In some embodiments, each U-shaped stator pair
1-12 is turned off (i.e., de-energized) when the flat blade 2628 is fully
aligned between the two legs of the stator (i.e., full closure). As
shown, two or four sets of stator pairs 1-12 (i.e., a total of four or
eight U-shaped stators) are energized at any given time.

[0260]FIG. 60 corresponds to FIG. 58 and illustrates the sequence that
each of stator pairs 1-12 is energized throughout the 360 degree rotation
of rotor 2626. As shown, two or four sets of stator pairs 1-12 (i.e., a
total of 4 or 8 U-shaped stators) are energized at any given time. Each
stator pair is on for 4/9 of the time (θon=0.444) and that
there are 12 stator pairs (npairs=12). Thus, it can be seen that the
fraction of time on (θon=0.444) for a rotor/stator
configuration of Option C1 is the same regardless of the number of stator
pairs. This is in sharp contrast to the traditional switched reluctance
motor in which the fraction of time on decreases as the number of stator
pairs increases.

[0261]FIGS. 61A-61C illustrate the stator width b for various
configurations of the flat blade/U-shaped core of Option C1. As shown in
FIG. 61A, for the 6/4 configuration, b is:

b = 2 π r 8 ( 84 ) ##EQU00072##

with a denominator of 8. The denominator for b is 16 for a 12/8
configuration (see FIG. 61B), and 32 for a 24/16 configuration (see FIG.
61C).

[0262]FIG. 62A illustrates a "unit cell" for a U-shaped stator 2700 for
use in a flat blade/U-shaped core rotor/stator configuration of Option
C1. The unit cell includes the wire bundle (coil) needed to provide the
magnetomotive force. Notice that a single unit cell including a pair of
stator legs 2702 and 2704 services a single flat blade. As the flat blade
passes between the magnetic legs 2702 and 2704, there is an attractive
force that acts to pull the magnetic legs 2702 and 2704 inward towards
the blade. Thus, by mechanically coupling sets of stator pairs together
as shown in FIG. 62A, a series of "magnetic legs" 2710 formed from two
abutting stator legs (e.g., legs 2704 and 2706) may be created, with the
magnetic flux flowing in the same direction through such abutting stator
leg pairs, as shown in FIG. 62B. To form a "magnetic leg" 2710, two
stator legs (e.g., legs 2704 and 2706) may be abutted and then the coils
may be wrapped around the pair of legs. The forces acting on a common
magnetic leg 2710 to pull the leg 2710 toward the flat blades on either
side of the leg 2710 will act in opposite directions so the net force
acting on the magnetic leg 2710 is zero or substantially zero. A net
force of zero eliminates movement of the magnetic leg 2710 and thus may
eliminate or reduce a source of vibration and noise.

[0263]Neglecting edge effects, the area of the core Ac relative to
the surface area of the rotor Ar at radius r follows:

[0264]FIGS. 63A and 63B illustrate a configuration Option C2, which is
similar to configuration Option C1, except the width of the core is
narrowed to b*, according to certain embodiments. FIG. 63A illustrates a
"unit cell" for a U-shaped stator pair 2720 of configuration Option C2,
and FIG. 63B illustrates a cross-section of the U-shaped stator pair 2720
if the U-shaped stator pair 2720 were laid-out flat.

[0268]FIG. 64 illustrates rotor/stator configuration Option D, which is a
flat blade/U-shaped core configuration 2800 including permanent magnet
blades, according to certain embodiments. Option D is generally similar
to Option C2, except that permanent magnet flat blades are placed on the
rotor in Option D. Thus, a motor formed in accordance with Option D may
be referred to as a permanent magnet motor (PMM).

[0269]In the example embodiment shown in FIG. 64, the rotor/stator
configuration 2800 includes a stator 2802 with eight U-shaped stator
pairs 1-8 and a rotor 2806 with six flat permanent magnet blades 2808.
Each U-shaped stator pair includes two legs, and the flat permanent
magnet blades 2808 pass through the gap formed between the stator legs,
e.g., as shown and discussed above regarding FIGS. 5-13 and 26A.

[0270]As shown in FIG. 64, the permanent magnet blades 2808 may be
positioned around the perimeter of rotor 2806 in alternating arrangement
of north (N) and south (S) magnets. At any given time, half of the stator
pairs (every other stator pair along the perimeter of stator 2802) are
energized with a north (N) polarity, and the other half of the stator
pairs are energized with a south (S) polarity. In this manner, the
permanent magnet blades 2808 are both pushed and pulled into alignment
with the nearest stator pair having the opposite charge, thus causing
rotor 2806 to rotate. As rotor 2806 continues to rotate, the polarity of
all eight stator pairs is switched simultaneously, back and forth between
north (N) and south (S) polarity. FIG. 64 illustrates eight positions of
rotor 2806 at 22.5 degree increments to show the rotation of rotor 2806.

[0271]FIG. 65 corresponds to FIG. 57 and the sequence that each of stator
pairs 1-8 is energized throughout the 360 degree rotation of rotor 2806.
Each stator pair is energized all the time (θon=1.0), but the
magnetic field switches directions.

[0272]In some embodiments, the blade magnets need not be particularly
strong because an area ratio Ago/Ac greater than 1 may be
used, which concentrates the flux density in the core. For example, as
shown in FIGS. 31 and 32, at an area ratio of 3, the flux density in the
blade is about 1/3 that of the flux density in the core. Thus, due to the
area ratio advantage, high torque may be generated using relatively low
strength magnets for blades 2808. Thus, relatively low strength (and thus
relatively inexpensive) magnets (e.g., Alnico magnets) may be used to
generate high torque. This class of magnets has the added advantage of
very high thermal stability.

[0273]With configuration Option D, an equal number of stators and blades
can be employed. For example, FIG. 64 shows an 8/8 configuration with
npairs=8. FIG. 61 shows that the stator width b is:

b = 2 π r 8 ( 104 ) ##EQU00088##

with a denominator of 8 for the 6/6 configuration, 16 for a 16/16
configuration, and 32 for a 32/32 configuration.

[0274]Because the stators are adjacent to each other, if multiple stator
sets are used in a particular machine, they may be configured as shown in
FIG. 63. In particular, the stator legs from one stator set may be
abutted directly against the stator legs from an adjacent stator set, and
wire coils may be wrapped around the abutted leg pairs. The ratio j is
defined as before:

This equation allows the independent specification of j,
Ago/Ac and a/b. The relationship for p is identical to
Option C2. The value for a is

a=(a/b)b (110)

From the unit cell (FIG. 63):

L*=2a+2m (111)

The radius where the force is applied is:

r f = r - A g o A c 1 2 aj ( 112 )
##EQU00094##

and ro is:

r0=r+d+a (113)

From Equation 44, an expression for d follows:

d = A w m = 1 m B c , m ax i ^ P 1 p
2 g μ o ( 114 ) ##EQU00095##

Sample Calculations

[0275]Provided below are sample calculations for determining the torque
density and power density generated by various configuration options
discussed above, including configuration Options A, B1, B2, B3, C1, C2,
and D. The calculations are based on the "unit cell" methodology
explained above such that the different configurations can be fairly
compared to each other, generally on a torque-per-physical-volume basis
or a power-per-physical-volume basis. In addition, the calculations are
based on example dimensions and other physical parameter values. It
should be understood that these dimensions and other values are examples
only and in no way limit the scope of any embodiments to such dimensions
or values.

[0279]Tables 1 and 2 summarize the torque density and power density,
respectively, resulting from the parametric evaluation of the seven
different configurations options. By examining Tables 1 and 2, the
following conclusions may be made: [0280]As the aspect ratio L/r
increases, the torque and power density increases. This occurs because
the unproductive wire wrap at the ends becomes a smaller percentage of
the entire device. [0281]As the number of stators increases, the torque
and power density increases. This results because the maximum flux
density of the core is limited to saturation. Arriving at the maximum
flux density over a shorter angular displacement causes the torque to
rise. [0282]Option B3>Option B2>Option B1 in terms of power density
and torque density. The differences are primarily due to the difference
in θon between these options. [0283]Option A has the advantage
of a much larger core area Ac than Options B1-B3. This advantage is
helpful with a smaller number of stators where Option A is always better
than Options B in terms of power density and torque density. With a large
number of stators, Options B2 and B3 can overcome Option A.
[0284]Compared to Option B3, Options C1 and C2 are more torque and power
dense because their area ratio Ago/Ac is greater than 1.
[0285]In Option A, the product of npairs θon=1 regardless
of the number of stators; therefore, as the number of stators increases,
θon must decrease. In contrast, with Options C and D,
θon is constant regardless of the number of stators. This
advantage dominates at large numbers of stators. [0286]There is an
optimal a/b for Options C1 and C2. [0287]There is an optimal j
(˜0.90) for Option D. For Option C2, the optimal j is 1. [0288]The
permanent magnet (Option D) has the highest torque density because
θon=1 and there are more stator pairs.

[0289]The above description has focused on applying this technology to an
electric motor in which electrical energy is converted to rotating shaft
power. The concepts may be equally well applied to generators in which
rotating shaft power is converted to electrical energy.

[0290]FIG. 66 illustrates an example system for cooling a rotor/stator
configuration 3000 (e.g., a switched reluctance motor or a permanent
magnet motor), according to certain embodiments. Rotor/stator
configuration 3000 may have any configuration disclosed herein (e.g., any
of Options A-D) or any other known rotor/stator configuration.
Rotor/stator configuration 3000 may include a stator 3002 including a
number of stator poles 3004, and a rotor 3006 including a number of rotor
poles 3008.

[0291]A housing 3010 may be provided for housing a cooling fluid. An end
portion of each stator pole leg (or stator pole for conventional SRM
configurations) 3004 may extend or pierce through a housing wall 3014 of
housing 3010. The interface between each stator pole 3004 and housing
wall 3014 may be sealed in any suitable manner to prevent cooling fluid
3012 from escaping housing 3010.

[0292]Housing wall 3014 may serve to isolate gases, indicated at 3020,
that may have a composition and/or pressure different than the
surrounding atmosphere. For example, housing wall 3014 may be used to
contain gases that are being compressed or expanded using a gerotor
compressor/expander, e.g., as described in any of the following United
States patents and Patent Application Publications: Publication No.
2003/0228237; Publication No. 2003/0215345; Publication No. 2003/0106301;
U.S. Pat. No. 6,336,317; and U.S. Pat. No. 6,530,211.

[0293]Because thermal energy is typically generated from electrical
resistance in the wire bundles, and hysteresis losses in the core, stator
3002 may become overheated. To prevent this possibility, stator poles
3004 may be immersed in a cooling fluid 3012 (e.g., gas and/or liquid),
as shown in FIG. 66. Cooling fluid 3012 may comprises an gas and/or
liquid suitable for providing heat transfer. In some embodiments, the
cooling fluid 3012 may be a heat transfer fluid that is (a)
non-electrical-conducting, (b) volatile, and/or (c) compatible with the
coatings on the coil wires (i.e., non-dissolving). In some embodiments,
cooling fluid 3012 may comprise a known refrigerant.

[0294]The thermal energy produced by operation of the device may cause the
volatile fluid 3012 to change phase from a liquid to a vapor, which phase
change removes thermal energy in the form of latent heat. Because the
liquid is boiling, the heat transfer coefficients may be very high, and
may thus prevent overheating of stator 3002. In some embodiments, the
vapors can be condensed in a heat exchanger 3026, which converts the
vapors back into a liquid. In essence, the system is a heat pipe, which
is one of the most efficient means for removing heat from systems.

[0295]FIG. 67 is a cut away view of a portion of the system of FIG. 66,
illustrating a portion of stator 3002 having a stator pole 3004 extending
through housing wall 3014, according to certain embodiments. Stator 3002
may have a laminar construction including a number of laminar metal
plates 3030. The laminations allow for the efficient conduction of
magnetic flux, while limiting electrical eddy currents that lower the
efficiency of the system. If the laminar metal of stator 3002 were
allowed to pierce through housing wall 3014, the laminate coatings may
provide a path through which the gases and/or liquids contained by
housing wall 3014 may leak. Thus, as shown in FIG. 67, the portion of the
stator pole 3004 that pierces through housing wall 3014 may be
constructed on non-laminar material. This non-laminar component of stator
pole 3004 is indicated at 3034. In addition, the joint between the
non-laminar portion 3034 of stator pole 3004 and housing wall 3014 may be
sealed in any suitable manner. For example, the non-laminar portion of
stator pole 3004 may be welded to housing wall 3014, which may be formed
from a non-magnetic material, e.g., stainless steel.

[0296]In addition, the laminar and non-laminar portions of stator pole
3004 may be intimately joined together in any suitable manner to
eliminate air gaps that would resist the magnetic flux between the two
stator pole components. For example, the two stator pole components may
be mechanically joined, e.g., using a dovetail joint 3040 shown in FIG.
67, welded, brazed, or otherwise joined.

[0297]In addition, in some embodiments, as shown in FIG. 68, thin slots
3050 may be formed in the non-laminar component 3034. The slotted portion
of component 3034 is indicated in the Front View by the dashed lines. The
slots 3050 in non-laminar component 3034 may be aligned in the same
direction as the laminations in the laminar portion of stator pole 3004,
and may serve the same purpose as the laminations (e.g., to reduce eddy
currents). The slot orientation shown in FIG. 68 may be used in various
rotor/stator configurations, including, for example, conventional SRM
configurations (e.g., configuration Option A) and U-shaped blade/U-shaped
core configurations (e.g., configuration Options B1-B3).

[0298]FIG. 69 illustrates an example configuration of a U-shaped stator
pair 3060 having two partially-laminar legs 3062 and 3064 extending
through housing wall 3014, according to certain embodiments. U-shaped
stator pair 3060 is generally laminar, except each leg 3062 and 3064 may
include a non-laminar portion 3034 extending through housing wall 3014,
e.g., to reduce the possibility of leaks across housing wall 3014, as
discussed above regarding FIG. 67. Non-laminar portions 3034 may be
connected to laminar portions of stator pair 3060, and to housing wall
3014 in any suitable manner, e.g., as discussed above regarding FIG. 67.

[0299]In this configuration, a flat blade 3070 passes between stator legs
3062 and 3064, as discussed above regarding FIGS. 5-13 and 26A. Flat
blade 3070 may be laminar in the orientation shown in FIG. 69. Thus, in
order to provide a continuous magnetic flux path, non-laminar portions
3034 stator legs 3062 and 3064 may include slots 3050 oriented as shown
in FIG. 69. For example, slots 3050 may turn or curve in order to align
with both (a) the laminar portions of stator legs 3062 and 3064 and (b)
the laminations of flat blade 3070. This slot orientation may be used in
various rotor/stator configurations, including, for example, various flat
blade/U-shaped core configurations (e.g., configuration Options C1, C2,
and D).

[0300]The short-flux-path configurations described with reference to the
various embodiments herein may be implemented for various SRM motors
and/or generators applications by changing the number of stator and rotor
poles, sizes, and geometries. Similar configuration may also be utilized
for axial-field and linear motors. Several embodiments described herein
(e.g., configuration Option D discussed above) may additionally be used
for permanent magnet AC machines where the rotor contains alternating
permanent magnet poles. Additionally, the embodiments described above may
be turned inside out and used as an interior stator SRM or BLDC machines,
with the rotor on the outside. These in turn can be used as motor,
generators, or both.

[0301]Numerous other changes, substitutions, variations, alterations, and
modifications may be ascertained to one skilled in the art and it is
intended that the present invention encompass all such changes,
substitutions, variations, alterations, and modifications as falling
within the scope of the appended claims.